Throttle response

Beamer · 1 Throttle response Sun Apr 10, 2016 7:50 am

Beamer

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Hi,

while trying to optimally set fuel mixture and mixture screw I'm unsure what to expect from a well tuned flying brick.

I have got the mixture as good as I can but if I snap open the throttle it is a bit knockey and a little slow pick up. It's pretty responsive but does not respond well if I really snap the throttle open.

Now these are quite heavy inertia motors, not proddy racing jap bikes, so this may be perfectly normal. Could some with more air miles advise on what to expect from one of these engines in good order?

Thx.

Snod Blatter · 2 Re: Throttle response Sun Apr 10, 2016 7:38 pm

Snod Blatter

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As far as I know, snapping the throttle open always results in a terribly underwhelming knocking rumbling noise with no more revs happening. Very disappointing.

duck · 3 Re: Throttle response Sun Apr 10, 2016 7:57 pm

duck

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I run the idle in the 12-1400 range on my Ks (vs the recommended 950 +/- 50) and they come off the line much better that way.

Holister · 4 Re: Throttle response Sun Apr 10, 2016 8:58 pm

Holister

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I've had a few issues with my idle for a while, but its now sorted. A rejig of the cable adjuster at the handlebars, TB balance thanks to Smithy and a tweek of the idle screw, it now runs where I want it. I found that 950 was a tad too low and now have it set to about 1000 (still experimenting). Even at 950 my throttle response was very good when snapped open but much smoother when set a little higher.

Rick G · 5 Re: Throttle response Sun Apr 10, 2016 9:59 pm

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Give then an extra 4° advance and see how responsive they are and how much more low end torque they have.

Beamer · 6 Re: Throttle response Mon Apr 11, 2016 2:39 am

Beamer

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Kapt. H wrote:Even at 950 my throttle response was very good when snapped open but much smoother when set a little higher.

OK, so it sounds like I may need a deeper level tune up to get that kind of response. Air filter, valve adjustment, throttle balance... the lot. It's hard to describe these things in an objective way. One man's 'good' may be another man's 'poor response'.

A throttle balance check may be a good idea but everything else needs to be in order first. I'll do a compression check. Maybe even head off, valve grind and piston ring check. But I don't have the possibility to go that deep right now.

Obviously any engine will pick up better if it starting from a higher tick-over. I suspect starting at 1200-1400 rpm is just masking the problem of a badly set up bike.

Rick. Did you mean 4° LESS advance? More advance certainly just increase the low end knocking and probably cause detonation under load. OTH that much extra retard will knock top end speed and fuel. Where are you getting these ideas from?

In any case I don't see a good reason for deliberately mis-setting the ignition timing by 4°

Beamer · 7 Re: Throttle response Mon Apr 11, 2016 2:55 am

Beamer

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I find this idea of using the mixture to set a tick-over speed as a number a bit odd. It does not seem to correctly specify the set up conditions.

My general experience with petrol engines would follow a method like adjust mixture screw to fastest tick-over then adjust in the direction weaker mixture until it starts to drop. Then ease back a tad.

If the tick-over mixture adjustment was giving me 1400 rpm I'd wonder what else needed looking at first.

There are two ways the tick-over will drop: too rich and too weak. You'd want to be on the too weak side. Also you are not heading for a specific number of rpm. You are looking for something defined by running conditions. There are a number of other factors that can affect what the tick-over will be, even with the correct mixture. Offsetting the mixture to compensate for another problem ( for example timing ) is just deregulating the motor further.

Rick G · 8 Re: Throttle response Mon Apr 11, 2016 3:39 am

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Advance the ignition timing 4° from standard which makes it 10° BTDC at base idle. It will give far better throttle response and more bottom end torque which makes it much easier to get going from a stop.
BMW as with most other manufacturers set the base idle ignition timing at 6°BTDC so the engines meet the polution control requirements. If you don't want to advance it past the recommended setting then that is your decision but please refrain from responding like you are saying I am talking shit. You may not mean it that way and I don't think you do but that is the way you are coming across and the reason you are getting into arguements.
I am getting these ideas from having worked for many years in the trade and for Honda Australia for 8 years in their own workshop and teaching many of the mechanics that they still employ.
I also built and drag raced Suzukis and Kawasakis for many years and was the No1 plate holder (National Champion) for 3 years running and retired in 1982 undefeated. I also built all my own engines and built and designed the frames for those engines.

Yes it may make some dfference to the top end HP but they will still run to the rev limiter in 5th, these are street bikes and I don't run flat out very often do you? So I find it much better to sacrifice some top end power that I would use maybe once in a year, maybe, for a far more rideable bike.

As to setting the idle speed with the air bypass settings you are still firmly stuck using a carb which relies on air flow to draw fuel through. EFI is a very different kettle of fish.
It is NOT a idle mixture screw but an air bypass for setting a fine flow of air past the throttle body while the throttle butterfly is fully closed. No idle air goes through the butterfly and the fuel is metered by the ECU.
If you start adjusting the idle by setting the butterfly position you will have nothing but idle speed problems, many have been caught out by think it works something like a carb.

Beamer · 9 Re: Throttle response Mon Apr 11, 2016 4:03 am

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Thanks for the informative reply Rick. That is what I wanted to know when asking where you get your information. Apologies if it came over as saying you were "talking shit", I was asking where you got these ideas and you gave a very helpful reply. There are so many people who throw out bad info on the internet and forums in general that it is very hard to know who or what to take seriously. We always have guess whether the person providing suggestions is a bar-stool mechanic or someone like yourself with top tuning experience.

My recent experience of burning out my HES captors because I took someone's information about testing them at face value has made me even more mistrusting and questioning. Sadly there seems to be more crap info than good and it's hard to know what is what.

That background is very helpful in knowing how to interpret what you write. Thanks.

Also the fuller explanation of why you suggested moving the std timing makes it a lot more credible and useful . You will appreciate that if someone pops up on a forum and suggests moving 4 deg extra from the manufacturer's spec. without saying why he thinks it is a good idea to ignore the manufacturer's spec. , we really are going to doubt whether it is a good idea.

I had intended to try inching the timing a little more advanced to see whether it would take it. Your information gives me more confidence about doing that, now you've given some more detail about the effects. Thanks for some useful input.

Beamer · 10 Re: Throttle response Mon Apr 11, 2016 4:14 am

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Rick wrote:It is NOT a idle mixture screw but an air bypass for setting a fine flow of air past the throttle body while the throttle butterfly is fully closed. No idle air goes through the butterfly and the fuel is metered by the ECU.

I'm a little confused by this. The bypass is bypassing the vane in the flow meter not the throttle butterfly.

The preload on the spring is probably designed to keep the vane closed at tick-over airflow and the EFI produces a fixed injection rate with no additional info from the AFM. The bypass screw determines how much air gets mixed with this fixed injection rate. This means that , in effect, it is similar to a carb air mixture screw. In a carb there is a small fixed jet and the air screw modulates the air flow to arrive at the correct mixture.

Unless I'm mistaken that seems to be essentially the same thing. ( I agree one should be careful not to draw too many analogies between carbs and injection systems ).

charlie99 · 11 Re: Throttle response Mon Apr 11, 2016 5:47 am

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yes you are totally wrong

there is air temp input, engine temperature input , revs input and a few other crazy things that can be established by just this information alone ....all before the flap opens .

K75cster · 12 Re: Throttle response Mon Apr 11, 2016 5:59 am

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A bit cheeky Charlie, he'll cotton to the bypass on the flap and the bypass on the throttle bodies, he's searching for clarity, I don't know enough to help him. I'm sure a re-read will bring to all to light

Beamer · 13 Re: Throttle response Mon Apr 11, 2016 6:25 am

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charlie99 wrote:yes you are totally wrong

there is air temp input, engine temperature input , revs input and a few other crazy things that can be established by just this information alone ....all before the flap opens .

Yes, there are temperature fine adjustments but none of that contradicts what I said about similarity of the mixture adjustments of both systems. Some carbs have cold start mechanisms too, that is beside the point as far as adjusting the mixture screw goes since all this should be done once the motor is at running temperature.

So far I don't see anything that make me totally or even partially wrong about the mixture screw being similar on both systems. Though I would be delighted if someone who has better knowledge can correct me.

Beamer · 14 Re: Throttle response Mon Apr 11, 2016 6:33 am

Beamer

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K75cster wrote:A bit cheeky Charlie, he'll cotton to the bypass on the flap and the bypass on the throttle bodies, he's searching for clarity, I don't know enough to help him. I'm sure a re-read will bring to all to light

Yes, I think Rick did not write quite what he meant. You are right I am seeking to clarify.

Rick wrote:No idle air goes through the butterfly

Unless there is another bypass that I'm not aware of, all air that enters the engine goes through the throttle butterfly.

My interpretation of what the two systems ( carb and injection ) do for idle running mixture seems very similar.

charlie99 · 15 Re: Throttle response Mon Apr 11, 2016 6:37 am

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yeah agree mate ...but to start by ignoring any past history or collective posts does no favour to the forum

for some the mystery of efi is a challenge ...and we could all benefit by understanding it a little more and I credit those for trying to understand

perhaps if the blog was posed as a series of questions ...with observed outcomes ...we could all assist ,,,?
I think its all about forgetting past historys with carburettor type machines (other than simple ergonomics like "fire. fuel , pressure and timing " )
and move onto what specifics noted and detailed by many contributors over many years here and else where .

these aren't new machines ...just new to some
some are trying to reinvent the proved wheel ...without noticing the wheel and how it was designed to work ,
I'm not surprised at outcomes so far

Rick G · 16 Re: Throttle response Mon Apr 11, 2016 9:27 am

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To be fair Charlie I think Beamer is trying to establish in his own mind how all this works.
Beamer I did not get the context fully and missed that you were refering to the bypass in the MAF
Its main purpose is to supply enough air for the idle bypass screws in each Throttle body to do their job and at the same time restrict flow sufficiently so that the barn door will react as soon as the butterflys open.
I am sure you have a good working knollege of how a carb works and that there are 2 ways of using an idle screw adjustment by metering air or fuel and they work in almost opposite ways. The method of adjusting the idle speed by the air bypass in the throttle bodies relies on the butterflys being closed fully so that air can be drawn through them.
One of the big problems we now have is that wear has taken its toll and things are starting to work not quite how it was intended.
The ECU or FICU meters the idle fuel regardless of how much if at all the idle bypass screws are open.
I first went through all this when Kawasaki released the Z750 with EFI which was the bosch LE-Jetronic and then again with Honda and I think the VF1000 was the first for them.
If you think the EFI systems on the bricks is a bit strange have a look at what Kawasaki called DFI (digital fuel injection) on the later ZN1300 six, now that stuff is strange. It was Kawasaki's first attempt at their own Fuel Injection.

So folks how about we try to put the bickering behind us and start over. I have been as guilty as anyone and actually managed to get a thread locked.
As the late great Oscar Wilde said about England and USA "two great countries separated by a common language". That's sort of what is happening here.

Beamer · 17 Re: Throttle response Mon Apr 11, 2016 10:34 am

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Thanks Rick, it seems were rather talking at cross purposes there. Similar terms for different things.

It seems that a lot of this is based on "all else being as it should be". In fact, probably nothing is quite right on a 20y old bike.

As I understand it the butterfly bypass screw is factory set and should not be used as a means of setting tick over. There may be a case for adjusting them if there is notable wear on the butterfly valve and it is leaking air past even when fully closed.

The screw on the butterfly linkage sets the tick-over by slightly opening the all the butterfly valves in sync. Tick-over is also affected by the idle screw on the AFM.

I set the latter using my carb ( screw on air-way type ) logic since it seems that it sets the idle richness in a similar way and the functional principal of going for fastest tick-over then moving towards weak until it starts to affect engine revs seems applicable however the richness gets changed. It is setting richness as a function of engine response.

This did work quite well. It may not yet be optimal and it may not be the officail "right" way to do it.

Do you see anything wrong with that or have a better method to suggest?

thanks.

Last edited by Beamer on Mon Apr 11, 2016 11:08 am; edited 2 times in total

Point-Seven-five · 18 Re: Throttle response Mon Apr 11, 2016 11:04 am

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Idle mix and speed is still a bit confusing to me, and I've been working around internal combustion for going on 50 years. Granted, for the last 20 odd years the technology has pretty much obviated the need to do a lot of messing about with automobile engines. Most of my time has been spent working on small marine engines diesel and gas. It wasn't until my reentry to BMW motorcycles that I was introduced to the intricacies of electronic fuel injection.

Beamer has introduced several topics that have inspired discussion that has increased my knowledge of the components and theory of fuel injection systems, at least as how they are applied to the motobricks.

Among others, I was at first put off by Beamers forum posts. However, with time, he appears to be fairly intelligent and has an inquiring mind and a willingness to ask questions and think out loud. Where I find him lacking is his social skills. He reminds me a lot of the guy who pops into a bar and starts talking loud about things he doesn't know and challenging those he really shouldn't. The kind of guy who, only if he is really lucky, won't end the night bloody in the parking lot.

I don't know how much time Beamer has spent in forums, but it appears to me he hasn't quite learned to spend some time lurking and learning who knows what they're talking about and the general tone of the discourse. It also doesn't hurt to kick one's civility and humility into high gear. It can certainly help to prevent what could be seriously embarrassing moments. It is to the credit of the members here that they have allowed him the time to become a contributing member who will add a lot to the overall knowledge base.

Rick G · 19 Re: Throttle response Mon Apr 11, 2016 11:29 am

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#3 is the adjustment for syncing the butterflys, they are the ones you dont touch unless you really need to like if you have had the whole setup apart.
#1 is the Idle adjustment screw and that bypasses air around the butterflys in the same manner as the bypass in the flow meter. If the butterfly is not closed completly the air pressure at the outlet of the bypass screw will be the same as the air pressure at both sides of the butterfly because the outlet is just on the engine side of the butterfly. On all the fuel injected engines I have ever worked on and that includes Honda and Kawasaki bikes and ford, GM and BMW cars the butterflys should be closed fully at idle and with the later injection (after about 1994) there is an air idle bypass that is controled by a stepper motor and that regulates the air bypassing the butterfly. I don't know about the later bikes but none of the bricks use a stepper motor to control idle.
The screw settings for syncing the butterflys usually don't need to be changed but with wear etc we have been seeing some that need to be adjusted. My K1100 is worn enough that #3 throttle doesn't set properly and the hot idle is around 1400rpm. I should fix it but have other things that are more important. I tried using 4 dial gauges and a drill shank to set them evenly but it's just simply worn too much.
One thing that is important to know when setting the butterflys is dont use the choke lever to set the position because it pulls on the #4 body where the main throttle cable pulls between #2 and #3 body and the slack built into the adjusters sets different openings from one to the other. It can be a real trap.

Any how its past midnight and if I dont get to bed I will turn into a pumpkin.

Beamer · 20 Re: Throttle response Mon Apr 11, 2016 11:32 am

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thanks for your thoughts ".75" I'm glad you've found my subjects have advanced your understanding. That's what it's all about.

The trouble with forums is that they don't work like a bar where most people don't start flaming because they know they may have to back it up. It's all too easy to start cussing at someone from the safety of the keyboard on the other end of the planet. Ending up bloody in the carpark is why most people tend to be more restrained when face to face.

That is why the forum rules here are pretty heavy on the "no swearing, no smoking" type policy with a double dose of be nice don't be aggressive etc. We should all bear that in mind, even if it is a while since some have agreed to the terms and memory may be fading.

Rick has shown it works. He said one of my comments did not read well but remained polite and calm, I politicised if it appeared rude. End of. On with useful exchanges.

I think I can help advance understanding AFM/EFI issues which are a troublesome black box to many owners. Thanks for the note of recognition. Wink

Beamer · 21 Re: Throttle response Mon Apr 11, 2016 11:45 am

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Rick wrote:One thing that is important to know when setting the butterflys is dont use the choke lever to set the position because it pulls on the #4 body where the main throttle cable pulls between #2 and #3 body and the slack built into the adjusters sets different openings from one to the other. It can be a real trap.

Thanks, I'd read that on another thread. Good trap to be aware of.

Auf keinen Fall den Chokezug dazu benutzen!! As they say in Germany Wink

#1 is the Idle adjustment screw and that bypasses air around the butterflys in the same manner as the bypass in the flow meter.

That's what I find odd. There is a central screw for setting the tick over. Why are these referred to as "Idle adjustment screw" ? Since there is one of these on each TB , they must serve for syncing the air flows ( separate from just the throttle valve itself ) in each cylinder, not setting the idle.

This will need to be done vacuum gauges or mercury columns. This is the sort of thing that requires a full top down service starting with compression an valve clearance checks.

Last edited by Beamer on Mon Apr 11, 2016 5:30 pm; edited 2 times in total

charlie99 · 22 Re: Throttle response Mon Apr 11, 2016 11:49 am

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Beamer wrote:

Unless there is another bypass that I'm not aware of, all air that enters the engine goes through the throttle butterfly.

My interpretation of what the two systems ( carb and injection ) do for idle running mixture seems very similar.

I do have an issue with the way that beamer makes statements rather than asking a question, as above . but ill get over it, I guess ...unreserved apologies to all .

I hope your explanation helps explain the above operation rick .

but it seems not.

the idle adjustment is usually performed at the throttle bodies ....not the idle up (choke activation) bar

there are 4 bypass screws in the throttle bodies which allow for air to bypass the throttle butterflys ...when adjusting these, the term "syncing the throttle bodies" . and is usually done with a manometer (or 4 ) on each of the throttle bypass vents with normally rubber caps on them ( the 4th one feeds the fuel pressure regulator and is closed to air normally )

have a look here
https://www.k100-forum.com/t1526-how-to-balance-the-throttle-bodies-solved

yes agree to both above ... lets hope things improve

looks like rick and I were on the same mission ,,,sorry for the double up

Point-Seven-five · 23 Re: Throttle response Mon Apr 11, 2016 12:02 pm

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One thing that I don't know and, for me, is the key to understanding the process of adjusting the idle speed, CO %, and mixture is what is determining the fuel injected at idle.

Is it a fixed amount so that the main air bypass on the flowmeter adjusts the overall mixture? This seems to be the case as the setpoint is determined by measuring the CO content of the exhaust. The only adjustable variable here is the air.

Is the amount injected controlled by idle rpm? Is there something in the system that tries to close the loop at idle/closed throttle around engine speed. If this is the case, when at idle, with the butterflies completely closed, the engine should either run at the preset speed or badly or not at all.

My experience with three k bikes seems to be that when the butterflies are closed, the idle air control screws on the throttle bodies have little or no control over fine tuning of idle speed. I can make the engine stall by closing them, but once they are open enough to run, the only effect they have is to balance the intake vacuum balance. Closing them down to pass less than the main air bypass will result in a richer mixture because the fuel flow is fixed(or is it?).

If the main bypass controls overall mixture and CO content, then it would be operating at cross purposes to use it to control idle rpm. If the throttle body idle air screws only balance the flow of the previously metered air they can't control speed. This is the crux of my confusion. What exactly do I adjust to get the desired idle rpm without upsetting the mixture?

Point-Seven-five · 24 Re: Throttle response Mon Apr 11, 2016 12:16 pm

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And just to throw another Spaniard in the works, does the throttle position switch have another function beyond the shutdown of fuel injection when closing the throttle at higher engine speeds.

Does it tell the Jetronic that the engine should be idling? If so, I would expect there is some logic in the system to close the loop on a preset idle rpm. I have never heard of this function in any description of Jetronic operation.

It does seem to me that this would be a desirable function and one the designers wouldn't overlook. In other words, the idle rpm is carved in resistors and an op amp and not user adjustable. It is what it is, and all we can do is screw up the optimum mixture by trying to adjust it.

"Lord, help me change the things I can, accept those I can't, and grant me the wisdom to know the difference."

Beamer · 25 Re: Throttle response Mon Apr 11, 2016 12:36 pm

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Charlie99 wrote:the idle adjustment is usually performed at the throttle bodies ....not the idle up (choke activation) bar

Thanks, I'd read the thread about syncing the throttle bodies. That is quite a complex operation.

From what you said above that is necessary each and every time there is a need to tweak the tick-over. That seems unnecessarily complicated. Why is this not done by adjusting the screw on the bar which operates all four mechanisms together?

The choke does indeed do this for cold starting ( ie. it temporarily increases the tick over ) but that does not mean that the adjuster screw has no purpose and this should not be used to adjust tick over.

Am I misreading what you wrote, or missing something about the way these adjustments work?

Beamer · 26 Re: Throttle response Mon Apr 11, 2016 12:48 pm

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Point-Seven-five wrote:And just to throw another Spaniard in the works, does the throttle position switch have another function beyond the shutdown of fuel injection when closing the throttle at higher engine speeds.

Does it tell the Jetronic that the engine should be idling? If so, I would expect there is some logic in the system to close the loop on a preset idle rpm. I have never heard of this function in any description of Jetronic operation.

It does seem to me that this would be a desirable function and one the designers wouldn't overlook. In other words, the idle rpm is carved in resistors and an op amp and not user adjustable. It is what it is, and all we can do is screw up the optimum mixture by trying to adjust it.

"Lord, help me change the things I can, accept those I can't, and grant me the wisdom to know the difference."

The EFI ( apparently ) does distinguish two situations : throttle shut at elevated rpm and at tick-over ( defined as <1200 IIRC ). The 'closed loop' action is possible since it does have input from the HES that detects rpm. During the former, it cuts injection totally; at tick-over it feeds a small injection of fuel. This is mixed according to restriction of air adjustments. It has no feedback on that variable. This means that the AFM mixture screw can affect tick over without the EFI fighting back.

I am inferring from this that EFI has a fixed rate of injection for tickover, until the vane in the AFM moves off base.

Presumably, by a similar argument, the adjuster of the bar on the throttle ramp can up the tick-over until the point ( 1200 rpm ) where the EFI wakes up and starts to affect things again.

At least that is what I have understood so far.

Beamer · 27 Re: Throttle response Mon Apr 11, 2016 12:59 pm

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.75 wrote:If the main bypass controls overall mixture and CO content, then it would be operating at cross purposes to use it to control idle rpm. If the throttle body idle air screws only balance the flow of the previously metered air they can't control speed. This is the crux of my confusion. What exactly do I adjust to get the desired idle rpm without upsetting the mixture?

My reading of this is:

TB balancing is rarely needed and is done only in exceptional situations ( total dismounting of mechanism , long term wear out of butterflies ).Normally factory set and paint marked : a good don't tamper indicator.

Tick-over mixture ( CO% ) is set by the mixture screw on AFM ( this will AFFECT rpm but is not the way to set it ).

Tick-over rpm is set by the screw on the throttle ramp. That would seem to be it's sole purpose.

I would not have thought that is controversial but if anyone has an informed counter argument I'll be happy to be corrected.

charlie99 · 28 Re: Throttle response Mon Apr 11, 2016 1:01 pm

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the injector shut off at deceleration is a typical efi management restriction placed on manufacturers to comply with pollution laws ...

charlie99 · 29 Re: Throttle response Mon Apr 11, 2016 1:03 pm

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Beamer wrote:

Tick-over rpm is set by the screw on the throttle ramp. That would seem to be it's sole purpose.

I would not have thought that is controversial but if anyone has an informed counter argument I'll be happy to be corrected.

keep reading grasshopper ,,,there is a lot to learn

Holister · 30 Re: Throttle response Mon Apr 11, 2016 1:29 pm

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Point-Seven-five wrote:........
My experience with three k bikes seems to be that when the butterflies are closed, the idle air control screws on the throttle bodies have little or no control over fine tuning of idle speed. I can make the engine stall by closing them, but once they are open enough to run, the only effect they have is to balance the intake vacuum balance. Closing them down to pass less than the main air bypass will result in a richer mixture because the fuel flow is fixed(or is it?).

If the main bypass controls overall mixture and CO content, then it would be operating at cross purposes to use it to control idle rpm. If the throttle body idle air screws only balance the flow of the previously metered air they can't control speed. This is the crux of my confusion. What exactly do I adjust to get the desired idle rpm without upsetting the mixture?

The way I understand it (and I'm no expert), when the idle adjustment screws are adjusted, the air mass changes and registers with the AFM. The FICU monitors and adjusts fuel accordingly. Correct fuel mixture is maintained. I don't see how fuel flow is fixed.
To balance the TBs, the butterflys need to be closed. To do that you need to screw the throttle adjustment out till it's just sitting off the stop. The idle adj screws are wound down till they seat (the engine may stall) and then out a quarter of a turn. From here they are adjusted with the aide of a manometer on each vacuum off-take till they are even. Then they can be adjusted up or down till you achieve the desired idle rpm. Then screw the throttle adjustment in till it juuust contacts the stop. Hope I got that right. :suspect:
What I'm not familiar with is whether or not there needs to be an adjustment of the AFM bypass to complete this procedure. Am I right in saying that the flap should be closed at at idle relying on the bypass to provide air?

....and if I could just add my 2 cents worth. I've participated in forums for many years and I've found this one to be the best I've come across. It's difficult using a medium like this to communicate. Not only do we miss a lot of the personal ques which help us to interpret what someone is trying to say but quite often people unintentionally project a personality which is not their normal self. We need to be aware, be patient, make allowances. Contributors aren't intentionally trying to be annoying. Personally, I would prefer to receive left-of-field contributions than hear abuse.
I'm sure everyone is appreciative of Rick's calm contributions as well as Charlie's gracious apology. Thanks fellas. And thanks also to beamer 'The Unruffled' for some very interesting and entertaining reading.

Cheers

Point-Seven-five · 31 Re: Throttle response Mon Apr 11, 2016 1:45 pm

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If indeed the rpm at idle is a fixed setting then closing the loop on it would require an adjustment to the amount of fuel injected. There is a small range for the exhaust CO spec so it could be that the very minor adjustments necessary to control speed would not take it out of range. I would guess that there would necessarily be a sequence to the tuning adjustments to prevent errors from being introduced.

There are two throttle body adjustments. One is to synchronize the butterflies and one to balance the intake vacuum. The butterfly synch adjustments are sealed with blue paint, are factory set, probably on a flow bench, and should be avoided if at all possible.

Intake vacuum synch, on the other hand, is something that can and should be done as part of any tune up. It is a simple procedure, and once the engine is warmed can be done in under 10 minutes using an apparatus as simple as a couple bottles with stoppers and some hose.

The throttle stop screw should not be used to set idle speed. It's purpose is to set the point where the butterflies are just closed so that they will open as soon as the throttle cable is pulled. The butterflies need to be closed so that the idle intake balance screws can do their job controlling the idle air flow. You should consider that adjustment to be a factory setting same as the butterfly synch screws. The more the butterflies are open, the less control over the throttle body balance the idle air screws on the throttle bodies will have. Comparing the cross sectional areas of the butterfly opening to the balance screw orifice it's apparent that it doesn't take much butterfly opening to upset the balance and thus the smoothness of the idle.

Point-Seven-five · 32 Re: Throttle response Mon Apr 11, 2016 2:09 pm

Point-Seven-five

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Kaptain Holister wrote:The way I understand it (and I'm no expert), when the idle adjustment screws are adjusted, the air mass changes and registers with the AFM. The FICU monitors and adjusts fuel accordingly. Correct fuel mixture is maintained. I don't see how fuel flow is fixed.

That is part of my confusion. According to the tuning procedures I have seen, the flap on the AFM is closed at idle. The main bypass sets the total amount of air available at idle, and the throttle body air screws distribute it evenly to the cylinders. It seems to me that if the amount of air allowed by the main bypass on the AFM is controlling the CO content of the exhaust the amount of fuel at idle is fixed or at least has minimum adjustment made to it by the FICU.

If the amount of fuel was being changed by the FICU it would be impossible to adjust a stable CO level with the air bypass.

To balance the TBs, the butterflys need to be closed. To do that you need to screw the throttle adjustment out till it's just sitting off the stop. The idle adj screws are wound down till they seat (the engine may stall) and then out a quarter of a turn. From here they are adjusted with the aide of a manometer on each vacuum off-take till they are even. Then they can be adjusted up or down till you achieve the desired idle rpm. Then screw the throttle adjustment in till it juuust contacts the stop. Hope I got that right. :suspect:

Sounds good to me. Only quibble I have is that I understand the basic balance opening is approximately 1.5 turns from seated. I could be wrong, though. I have seen the number of turns stated as anything from your 1/2 turn to as high as 2.5 turns. What I have observed on my bikes is that down to a very small air screw setting there is little or no change in idle speed until the engine is strangled by lack of air.

What I'm not familiar with is whether or not there needs to be an adjustment of the AFM bypass to complete this procedure. Am I right in saying that the flap should be closed at at idle relying on the bypass to provide air?

Yes! Opening the flap will reduce the control available through the main bypass adjustment. The main bypass should be the first adjustment to be fine tuned as it sets the basic fuel/air mixture for an optimum exhaust CO content of 2%. From what I have read in other places this 2% setting is important in having the optimum mixture at mid-rangge throttle settings.

When that adjustment is made, I assume that the throttle body air balance screws have to be open enough so that they are not the limiting factor in the airflow at idle. If they are closed enough to limit airflow they will not allow the main air bypass to set the CO content of the exhaust.

Beamer · 33 Re: Throttle response Mon Apr 11, 2016 2:17 pm

Beamer

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.75 wrote:The throttle stop screw should not be used to set idle speed. It's purpose is to set the point where the butterflies are just closed so that they will open as soon as the throttle cable is pulled.

OK, the butterflies could never be more than shut, but perhaps the screw provides a physical stop and thus protects the throttle bodies from wearing. Sounds reasonable. Thanks.

Beamer · 34 Re: Throttle response Mon Apr 11, 2016 2:26 pm

Beamer

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Kapt H wrote:The way I understand it (and I'm no expert), when the idle adjustment screws are adjusted, the air mass changes and registers with the AFM. The FICU monitors and adjusts fuel accordingly. Correct fuel mixture is maintained. I don't see how fuel flow is fixed.

I don't think so.
The amount of air passing when at tick-over is not enough to open the vane of the AFM against the spring preload. There is no adjustment possible since the EFI had no input about the air flow until the vane moves off base posn. This allows manual adjustment of the mixture with the AFM screw.

Then screw the throttle adjustment in till it juuust contacts the stop. Hope I got that right.

That agrees with what I said just above about this being a physical stop to prevent the butterflies bottoming out on the TBs themselves.

Beamer · 35 Re: Throttle response Mon Apr 11, 2016 2:41 pm

Beamer

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.75 wrote:Yes! Opening the flap will reduce the control available through the main bypass adjustment. The main bypass should be the first adjustment to be fine tuned as it sets the basic fuel/air mixture for an optimum exhaust CO content of 2%. From what I have read in other places this 2% setting is important in having the optimum mixture at mid-rangge throttle settings.

When that adjustment is made, I assume that the throttle body air balance screws have to be open enough so that they are not the limiting factor in the airflow at idle. If they are closed enough to limit airflow they will not allow the main air bypass to set the CO content of the exhaust.

What you say makes sense but there is a contradiction in this set up process. If the TB bypass screws are to set the tickover speed they are dominating the air flow and thus the idle mixture. Then AFM mixture screw cannot do this.

This brings me back to thinking that TB screws are to *balance* the idle air flow to ensure smooth running, not the idle mixture. This means that central screw is not just a physical stop but should be used to set ticker speed.

That is what my Joe Public workshop manual says too. ( Pinch of salt )

What does the official BMW workshop manual say?

Point-Seven-five · 36 Re: Throttle response Mon Apr 11, 2016 2:43 pm

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Is there a voltage from the flap at the closed position that is used to set the amount of fuel at idle?

This would be a good way to design a system that would be readily adaptable to a lot of different size engines with different idle speeds.

Beamer, what did you find when you did your measurements on the flap wiper output? (Oooh, that sounds nasty!) :cyclops:

Point-Seven-five · 37 Re: Throttle response Mon Apr 11, 2016 2:56 pm

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Beamer wrote:

.75 wrote:When that adjustment is made, I assume that the throttle body air balance screws have to be open enough so that they are not the limiting factor in the airflow at idle. If they are closed enough to limit airflow they will not allow the main air bypass to set the CO content of the exhaust.

What you say makes sense but there is a contradiction in this set up process. If the TB bypass screws are to set the tickover speed they are dominating the air flow and thus the idle mixture. Then AFM mixture screw cannot do this.

As far as I can tell, the throttle body bypass screws do not set idle speed. They can strangle the airflow to slow the engine with an overly rich mixture, but their real reason for being is to adjust the air flow to each individual cylinder.

This is why I believe they should be open the same across all cylinders and open enough that as a group they do not limit the airflow to less than what the main bypass allows.

This brings me back to thinking that TB screws are to *balance* the idle air flow to ensure smooth running, not the idle mixture. This means that central screw is not just a physical stop but should be used to set ticker speed.

Yes, they balance the airflow to each cylinder. Since we can assume the injector for each cylinder is putting out the same amount of fuel as the others, the mixture will be uniform across all the cylinders and the engine will be idling smoothly with minimum combustion variation from cylinder to cylinder.

Any imbalance in airflow causes an improper mixture in that cylinder.

Beamer · 38 Re: Throttle response Mon Apr 11, 2016 3:02 pm

Beamer

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There is fixed floor to the output voltage, which is set by the laser trimmed resistor chain.

There is what I've called a dead zone where the vane can move like 1mm without the ouput voltage changing. This is adjustable but has a spot of thermal glue to lock it as standard. Like the sync this is factory set and should not be moved unless you've messed around with the resistor plate ( to get a clean track ) or you suspect there is spring fatigue or other long term degradation which need compensating for.

This dead zone seems to be useful a tuning parameter as I have described in the flowmeter thread.

PS check your use of quotes, your last two posts have had your text inside the quote of others.

Beamer · 39 Re: Throttle response Mon Apr 11, 2016 4:09 pm

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In the diagram of injector ramp that Rick provided above, we see screw #2 called "main throttle adjustment screw".

https://servimg.com/view/17702881/188

So what part of the throttle behaviour is this supposed to adjust ?

The individual screws on each TB are labelled "idle adjustment screw" So what part of the idle is this supposed to adjust?

It seems that certain people are reading the latter to mean that this is how you are supposed to adjust bike's tick-over rpm. However, it does not seem logical to me the have four separate screws for this function. Clearly, these throttle bypass screws are to balance the air flows under idle conditions.This is probably necessary since the throttle butterfly sync is not precise enough; It works fine for higher regimes but when the bf valves are only just open a small difference makes a huge %age difference to air flow. Thus the need for a bypass screw to tweak them in and get a nice, smooth running tick-over.

It is the "main throttle adjustment screw" that is intended to provide the "main throttle adjustment" , ie tick over engine speed.

Point-Seven-five · 40 Re: Throttle response Mon Apr 11, 2016 5:03 pm

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First of all, when I respond to multiple points you will notice that the quote is in italics and my response is normal text. Makes answering multiple points easier.

I haven't the slightest idea how we are expected to control idle speed. Fuel delivery is not adjustable as far as I know when the engine is idling. Idle speed is whatever the engine does when the air delivery is correct for the amount of fuel being delivered. So far, on my three bikes, the idle speed is between 900 and 1050 rpm and varies a bit with engine temperature and how I'm riding. Whatever it is, I can live with it. In fact, when it's around 950 rpm I'm happy because I can be pretty sure everything is working right.

It's important to have clean injectors so the fuel delivery is accurate and correct. I wonder sometimes what using different model injectors do to the idle. Apparently, they don't mess things up because you hardly ever hear of people having trouble when they do stuff like going to 4 hole injectors. Maybe the amount of fuel isn't that critical at idle.

Beamer · 41 Re: Throttle response Mon Apr 11, 2016 5:10 pm

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http://technik.flyingbrick.de/images/d/df/13_Falschluft.pdf

Those screws are called Umluftschrauben in German. That means bypass screw ( as correctly stated by Rick ) , not "idle adjustment screws as incorrectly labelled in the diagram he linked above.

It seems that there is some sloppy translation going on by people who not understand the function of these screws and are just guessing and making names up. This then gets amplified by a game of internet chinese whispers.

Here is a diagram from another pdf calling itself "BMW_K75_K100_Repair_Manual" that I found on another BMW owners site ( which shall remain nameless )

Not a single one of those items is correctly labelled. This is getting beyond a joke.

I'm not surprised that there is a lot of confusion around. :shakes head:

Last edited by Beamer on Tue Apr 12, 2016 1:44 am; edited 5 times in total

Beamer · 42 Re: Throttle response Mon Apr 11, 2016 5:13 pm

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.75 wrote:Apparently, they don't mess things up because you hardly ever hear of people having trouble when they do stuff like going to 4 hole injectors

I assume that people would replace injectors with ones which provide the same flow rate, even if they are different structure or manufacturer.

Fuel delivery is not adjustable as far as I know when the engine is idling. Idle speed is whatever the engine does when the air delivery is correct for the amount of fuel being delivered.

Yes, I suspect you may be correct. Which means the only way to affect it a bit is to deregulate the mixture using the AFM bypass. This seemed odd to me earlier but may be the only control we have ( if that is the right word for it). In fact the reason it seems odd is that it is not a valid way to set the idle engine speed in the first place.

That would also mean that my manual is incorrect about the central screw on the ramp, but that would not surprise me enormously. I'm getting to the stage when I'm more surprised if I get some good information.

So that brings me back to what I suggested earlier: adjust the AFM bypass for max rpm. Then find the range where it remains stable ( which is quite large ) and either go to rich end, weak end or guess the middle. I still don't see a reason not to follow what I suggested earlier by carburettor analogy: going for the weak end of the range that gives max rpm.

Like I say it worked well in practice. I suppose all that can be done beyond that is to check with a gas analyser.

Point-Seven-five · 43 Re: Throttle response Mon Apr 11, 2016 7:16 pm

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Your idea of going for the "weak" end of the range is a common tuning technique. It has been written up since about the late 90's, for the K bikes and is referred to as the "lean drop method". It's the same idea as what we did when I ran enduros long ago. Back then it was referred to as tuning for "lean best idle". It's still how I set idle mixtures on the sailboat gasoline auxiliaries I work on. I like it because it gives the lowest chance of fouling the plugs on a slow turning engine that seldom reaches temperatures above 160 degrees F.

Assuming a fixed fuel rate at idle from the Jetronic system that is set to yield a nominal idle speed of 950 rpm I would figure that I am in the ball park when that is what the engine is turning. I realize that wear and tear on the parts can upset the flow rates of fuel and air. For that reason, I always have the option of working by taking plug readings which is something I may need to do as at least one of my bikes is starting to show signs of running rich.

Beamer · 44 Re: Throttle response Mon Apr 11, 2016 7:31 pm

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Your idea of going for the "weak" end of the range is a common tuning technique. It has been written up since about the late 90's, for the K bikes and is referred to as the "lean drop method".

Thanks. Not sure it got met with such derision earlier. It works.

Rick G · 45 Re: Throttle response Mon Apr 11, 2016 9:29 pm

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I am going with what I was taught by Kawasaki about the system used on the Z750 which was their first and I believe the first EFI motorcycle engine produced.
The air bypass at the Air flow meter or as Bosch call it the MAF (Mass Air Flow) is set at the factory and will most likely never need to be changed so leave it alone.
The voltage from the MAF tells the ECU when the engine is at idle the Throttle Position Sensor TPS tells the ECU to cut fuel above 2000rpm. This is why we can change the position of the TPS and get around the annoying low speed 1st gear kangaroo hop feature and still get a good idle as it was intended to be done.
To set the MAF air bypass first the bypass screw is opened past where it should be set so as to make sure the engine does get enough air at idle. The amount of fuel injected at idle is fixed and is determined by the ECU.
The idle speed is set by adjustment of the air bypass adjustment screws or Big Brass Screws (BBS is the tech term) and according to factory with the Kawasaki was 1000 rpm and BMW 950rpm. When these adjustment screws are in the correct position to give that idle speed the CO2 should be 2%. If the throttle butterflys are not fully closed or there is significant wear you will most likely not attain the 2% CO2 reading.
Once the idle is set then you obtain the correct setting on the air bypass at the MAF by screwing the screw in till the engine starts to falter or the CO2 reading goes up from 2% then back it out till the idle speed is once again at 1000rpm or 950 rpm for the BMW and the engine is running smoothly then go a futher 30° to 45°. and this will allow the flap or Barn door as it is more commonly called to react as soon as the throttle is opened and more air is required.
A CO@ reading of 2% will show that the idle adjustments are over all correct but will not allow you to get a smooth idle which in my cynical opinion only keeps the customer satisfied by not showing up the rattles which both brands are noted for.
There is a very slight enrichment takes place when the throttle is initially opened because the Vacuum drops and the fuel pressure regulator goes to a marginally higher pressure which makes for a very slight enrichment but this was never good enough to over come the dead spot if the throttle was opened very quickly. With BMW this feature was continued on to the motronic 2.1 in the 16v RS but discontinued with the K1100 probably because it was not effective.

Beamer · 46 Re: Throttle response Tue Apr 12, 2016 1:40 am

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Rick wrote:There is a very slight enrichment takes place when the throttle is initially opened because the Vacuum drops and the fuel pressure regulator goes to a marginally higher pressure which makes for a very slight enrichment but this was never good enough to over come the dead spot if the throttle was opened very quickly.

Thanks Rick. That is what this thread was initially started to ask about.

It seemed quick likely to me that I was not going to get instant, fast throttle response on an engine like this but I wanted confirmation from those with air-miles flying bricks.

There is also a feature to momentarily richen the mixture during hard acceleration, that is overshoot in the AFM vane position but this is a double edged sword: it also takes time to build up speed ( perhaps .25 to .5 seconds ) since there is quite a bit of inertia in the metal vane. This mean it will be too weak initially and physically can not respond instantly.

The air bypass at the Air flow meter or as Bosch call it the MAF (Mass Air Flow) is set at the factory and will most likely never need to be changed so leave it alone.

To set the MAF air bypass first the bypass screw is opened past where it should be ....

Sorry, I'm confused. This seems to contradictory. Are you saying it shouldn't need moving ... but if you really want to, this is how?

Thanks.

Beamer · 47 Re: Throttle response Tue Apr 12, 2016 1:51 am

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Rick wrote: This is why we can change the position of the TPS and get around the annoying low speed 1st gear kangaroo hop feature and still get a good idle as it was intended to be done.

Are you referring to adjusting the switch so that it never clicks in to signal throttle closed to the ECU?

I have managed to get the K75 slow running perfect with a combination of setting the amount of dead zone on AFM wiper and adjusting the AFM mixture screw.

It is perfectly smooth opening up and cutting the throttle as one does in traffic or at junctions. It is a real pleasure to ride now. It also fixed the annoying lag that I had when I opened up going into a bend. No kangaroos here ( but this is in Europe , no marsupials Wink

)

I describe how I adjusted and measured that at the end of the flowmeter thread.

https://www.k100-forum.com/t10996p50-flowmeter-restoration#131627

Rick G · 48 Re: Throttle response Tue Apr 12, 2016 3:00 am

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"Are you saying it shouldn't need moving ... but if you really want to, this is how?"

Yes that is how to do it if you need to do it.

If you set the switch correctly the problem is very minor but as wear takes it's toll and a succession of owners play with settings that they know nothing about, it is an easy way to get rid of an annoying problem.

Point-Seven-five · 49 Re: Throttle response Tue Apr 12, 2016 10:56 am

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Beamer, I'm not sure I followed you explanation of how your AFM is now set up. With regard to the smoothness at low speeds, is it the reduction in dead band as the door is opened that makes the improvement? My K75RT is difficult to control in stop and go traffic and I would really like to smooth things out, what with the lurch and the front end diving.

Can you just post a list of what you changed to get the present configuration without explanation?

Point-Seven-five · 50 Re: Throttle response Tue Apr 12, 2016 11:08 am

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With 75,000 miles on my K75RT I am starting to see evidence of a rich fuel mixture in my plug readings and would like to see what can be done to clean things up a bit. I know it's not oil fouling because she uses virtually no oil(1 qt/3000 miles).

Doing a valve adjust this week, then a good tuneup and off to find someone who will do a sniff on my exhaust. I have a spare AFM and think it might be useful to do your mods to it.

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