1989 K100RS SE Won't Start

Point-Seven-five · 1 1989 K100RS SE Won't Start Tue Feb 25, 2020 12:00 pm

Point-Seven-five

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Last September I bought a non-running 1989 K100RS SE with ABS basket case that had 48,000 miles. The seller told me it had been sitting for about 10 years in the back of a BMW dealer's shop before he got it and put it in his garage for an additional 2 years.

I did a fairly extensive restoration on it, and when I was done it started easily and ran well. After several running sessions and a couple of very short rides(only a mile or two, bike has no plates) I put it away for the winter in November

In early January I tried to start it to charge the battery and circulate the oil, but no joy. The engine flooded and the spark plugs came out sooty and wet. After cleaning the plugs, the engine started, but had a lot of trouble, running on one or two cylinders, backfiring, missing, and dumping fuel out of the joint between the header pipes and the silencer. After a couple minutes of struggling, the engine begins to fire a little more consistantly and once it is finally able to warm up it runs smoothly, and starts easily.

Next day I try to start, and it's back to flooding again.

The bike has new:

Fuel injectors
Fuel pump
Fuel filter,
Fuel lines
Fuel pump mounting
Fuel level sender and pump wiring
Spark plugs
Air filter
Z-tube

The tank has been thoroughly cleaned and filled with fresh non-ethanol premium fuel. The fuel rail has been thoroughly cleaned and the electrical connections have all been cleaned with Deoxit. The injectors pulse and spray a good pattern when the engine is cranking. The fuel pressure regulator provides a steady 36psi to the rail and holds pressure for at least 30 seconds when the engine is stopped.

The hall effect sensors are good and the timing is correct. The coils check good resistance and the plug wires have the proper resistance from the coil connection through to the center electrode of the spark plug when it's plugged into the cable. Spark on all plugs is strong when the plugs are clean, and a bit weaker when they are wet and fouled.

Valve clearances were set to .008 intake and .012 on exhaust, the air bypass screws were set to 1 1/2 turns out and then adjusted to balance the throttle bodies. Idle was set to 1000rpm.

AFM has been checked and cleaned. It now gives proper resistance readings per Bert's troubleshooting guide. Air temperature and water temperature have been checked numerous times and give proper readings every time both at the sensor terminals and the EFI plug. All terminals have been cleaned with Deoxit.

Compression is good and the engine burns no oil. The battery is kept charged and the starter turns the engine vigorously. The tachometer is working properly. The electrical system is working properly with the alternator charging the battery.

This has me totally stumped, I have no idea where to look next. None of my searches point me to anything else I can look at. I understand the Jetronic has some sort of rich starting setting built in that controls injection until the engine fires. Is this starting mixture adjustable somehow, or do I need to replace the Jetronic box? I really don't want to spend the money to get another one if I don't have to.

92KK 84WW Olaf · 2 Re: 1989 K100RS SE Won't Start Tue Feb 25, 2020 12:24 pm

92KK 84WW Olaf

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I wonder.....clutch switch or neutral light gone faulty?

You have mentioned virtually all known trouble areas but not these and you don't have a side stand switch. However these induce a no start, as opposed to a bad start/running badly so unlikely to be your problem.

Fuel pressure regulator uses a diaphragm and after sitting so long could also be faulty and result in massive over fuelling/flooding but your test on that would seem to confirm its ok.

However what you are describing is more like over fuelling that sorts itself out as the engine temperature rises.

Anyone near you that you run a quick swap of the Jetronic unit to check it out?

When you replaced the temperature sensor as in the one behind the radiator [or did you?] is it set in ptfe tape? If you took readings while it was in the bike and they were good then you may be ok, but if not this could be an issue as ptfe tape blocks the grounding through the engine casing and will cause this too.

New injectors.....same type?

Can you run a check to see if the are staying open? If all cylinders are flooding you are looking at something up the line that controls fuelling to all injectors, rather than the injectors themselves.

Last edited by 92KK 84WW Olaf on Tue Feb 25, 2020 12:25 pm; edited 1 time in total

Point-Seven-five · 3 Re: 1989 K100RS SE Won't Start Tue Feb 25, 2020 1:44 pm

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Olaf, I have a fuel pressure test gauge plumbed into the return line and it reads a pretty steady 36psi when the engine is cranking and running.

Yes, the over fueling seems to gradually sort itself out after stumbling, backfiring, etc for about 3-4 minutes. then as long as the engine is warm, it will start easily and run fine.

There is no one nearby with a 4 cylinder Jetronic that I know of.

I have tested the water temperature sensor both at the Jetronic connector and at it's own terminals and I get correct resistance readings at both places. I have cleaned the terminals with Deoxit, but have not removed it. It appears to have a good ground from the sensor body to ground.

I bought the injectors on ebay, and yesterday contacted the seller who confirms that they flow the correct amount of fuel which is 14 pounds/hour. He claims to have sold many sets with no problem and has a good feedback rating.

I pulled the injectors and rail from the head and confirmed that they all pulse and spray fuel when the engine is cranked.

I'm beginning to think the problem is in the Jetronic, but have no idea what to look for.

MartinW · 4 Re: 1989 K100RS SE Won't Start Tue Feb 25, 2020 2:46 pm

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.75 when you get it running and it only runs on two cylinders are those cylinders supplied by the same coil? Do you have a good strong spark on all four cylinders?
Regards Martin.

92KK 84WW Olaf · 5 Re: 1989 K100RS SE Won't Start Tue Feb 25, 2020 2:55 pm

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MartinW wrote:.75 when you get it running and it only runs on two cylinders are those cylinders supplied by the same coil? Do you have a good strong spark on all four cylinders?
Regards Martin.

Now you got me re reading this and MartinW is right on the money....been there.

No cost option is check which two cylinders are running when you fire up, ye old hand on exhaust to see which headers are cold....it will be either 1/4 or 2/3 if its a coil issue. Then swap the two coils, they are interchangeable. If the problem follows the coils its the coils are the problem and one needs to be replaced. If the problem does NOT follow the coils likely to be HES Hall sensor but a possible ICU fault. If its any other combination plug leads/caps/plugs are cause.......

MartinW · 6 Re: 1989 K100RS SE Won't Start Tue Feb 25, 2020 3:11 pm

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Olaf one of the best multipurpose diagnostic tools I have bought was a digital laser thermometer. You can check header temperature, coolant temperature and fuel temperature and they can also detect Zombies. They are now around the $10.00 Plus mark.
Regards Martin.

Point-Seven-five · 7 Re: 1989 K100RS SE Won't Start Tue Feb 25, 2020 3:11 pm

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Martin, that is a good question. So far I have used an infrared thermometer on the headers and it appears that the misfire is not consistent to particular cylinders. Temperatures on the headers didn't vary all that much when I checked them, but it did appear that the pipes for #2 and #3 were a bit cooler than #1 and #4.

I suppose that may point to a coil problem, but after an overnight cool down following the engine running none of the cylinders fire until I clean the plugs. I can't get a single pop from any of the cylinders.

I think I'll clean the plugs and get another temperature reading on the headers.

Stay tuned.

Point-Seven-five · 8 Re: 1989 K100RS SE Won't Start Tue Feb 25, 2020 3:16 pm

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Following Olaf's latest post I think that he may be on to something. I think I'll take a run into town for new plugs and run a temperature test this evening. Will set up a fan to cool things between runs and do the coil swap thing.

It wouldn't be the first time I've seen a coil give me a spark with the plug out of the cylinder, but not under compression.

MartinW · 9 Re: 1989 K100RS SE Won't Start Tue Feb 25, 2020 3:20 pm

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I haven't used it much but I do also have a inline spark plug tester. https://www.aliexpress.com/item/4000065838620.html?spm=a2g0o.productlist.0.0.57951c32ZOoWp2&algo_pvid=63bf7fed-c8ca-4fe7-8dd1-01b1cb2d2421&algo_expid=63bf7fed-c8ca-4fe7-8dd1-01b1cb2d2421-10&btsid=0ab6fa7b15826580392948960e715e&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_
Regards Martin.

indian036 · 10 Re: 1989 K100RS SE Won't Start Tue Feb 25, 2020 5:03 pm

indian036

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Point-Seven-five wrote:Olaf, I have a fuel pressure test gauge plumbed into the return line and it reads a pretty steady 36psi when the engine is cranking and running.

I hope "return line" was a brain fade or typo. The return line shouldn't have any significant pressure, as it is just returning fuel to the tank.

The 36psi should be on the pressure line, either between tank outlet and fuel rail (easiest access) or fuel rail and pressure regulator.

Bill

Point-Seven-five · 11 Re: 1989 K100RS SE Won't Start Tue Feb 25, 2020 6:56 pm

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Yes, the gauge is plumbed in between the rail and the regulator. I was thinking with regards to the rail.

Went into town for a fresh set of NGK plugs, but found that there are none and I have to go back tomorrow morning after 8am. Looks like I'm shut down for the night.

Rick G · 12 Re: 1989 K100RS SE Won't Start Tue Feb 25, 2020 7:27 pm

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Sounds like the temperature sender to me. Have you pulled it out and cleaned the copper washer because they can get a build up of copper oxide which is conductive in one direction like a diode. I think it was Charlie that had a problem like that some years ago. The thread being Brass will do the same.

92KK 84WW Olaf · 13 Re: 1989 K100RS SE Won't Start Tue Feb 25, 2020 7:49 pm

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RicK G wrote:Sounds like the temperature sender to me. Have you pulled it out and cleaned the copper washer because they can get a build up of copper oxide which is conductive in one direction like a diode. I think it was Charlie that had a problem like that some years ago. The thread being Brass will do the same.

Also........ don't the use ptfe tape when fitting it.

Rick G · 14 Re: 1989 K100RS SE Won't Start Tue Feb 25, 2020 8:47 pm

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92KK 84WW Olaf wrote:

RicK G wrote:Sounds like the temperature sender to me. Have you pulled it out and cleaned the copper washer because they can get a build up of copper oxide which is conductive in one direction like a diode. I think it was Charlie that had a problem like that some years ago. The thread being Brass will do the same.

Also........ don't the use ptfe tape when fitting it.

Should never use PTFE tape on a parallel thread only tapered threads.
Had a goon use it on some parallel threads on a truck brake system and the treadle valve got some tape in it and leaked so the brakes were binding with very costly consequences.

Point-Seven-five · 15 Re: 1989 K100RS SE Won't Start Wed Feb 26, 2020 12:40 am

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Having built high pressure hydraulic systems for several years when I was younger, I was edumacated early on about when to use or not use teflon tape. No need if there is a gasket or o-ring to seal the fitting.

The water temperature was the first thing I suspected when I pulled wet spark plugs. I've checked the resistance numerous times both at the sender and the big Jetronic connector and so far it checks out every time. With the mess I can have with leaking coolant when I pull the sender out, I'm inclined to let sleeping dogs lie as long as I am not seeing any bad resistance readings. The sender and the standpipe it is installed in are in pretty good shape with minimum corrosion. I did hit the sender and the connector terminals with Deoxit.

With the diode effect I think I will go back and recheck the resistance of the sender from both directions with my meter. I guess I should see the same resistance regardless of probe polarity.

indian036 · 16 Re: 1989 K100RS SE Won't Start Wed Feb 26, 2020 1:29 am

indian036

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Point-Seven-five wrote:Yes, the gauge is plumbed in between the rail and the regulator. I was thinking with regards to the rail.

92KK 84WW Olaf · 17 Re: 1989 K100RS SE Won't Start Wed Feb 26, 2020 7:14 am

92KK 84WW Olaf

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Point-Seven-five wrote:Having built high pressure hydraulic systems for several years when I was younger, I was edumacated early on about when to use or not use teflon tape. No need if there is a gasket or o-ring to seal the fitting.

The water temperature was the first thing I suspected when I pulled wet spark plugs. I've checked the resistance numerous times both at the sender and the big Jetronic connector and so far it checks out every time. With the mess I can have with leaking coolant when I pull the sender out, I'm inclined to let sleeping dogs lie as long as I am not seeing any bad resistance readings. The sender and the standpipe it is installed in are in pretty good shape with minimum corrosion. I did hit the sender and the connector terminals with Deoxit.

With the diode effect I think I will go back and recheck the resistance of the sender from both directions with my meter. I guess I should see the same resistance regardless of probe polarity.

A little thing...when you pull the sender out. Just confirming it is the one behind the radiator as there are two on the bike.....

Point-Seven-five · 18 Re: 1989 K100RS SE Won't Start Wed Feb 26, 2020 9:37 am

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Olaf, yes, it's the one that's carefully hidden between the air boxes and the radiator with the connector that has that damn wire. Speaking of that wire, would it be okay to just leave it off?

I have a replacement MAF that I'm going to install this weekend. As long as I'm in there again, I'll take another look at that temperature sender.

92KK 84WW Olaf · 19 Re: 1989 K100RS SE Won't Start Wed Feb 26, 2020 10:22 am

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Point-Seven-five wrote:Olaf, yes, it's the one that's carefully hidden between the air boxes and the radiator with the connector that has that damn wire. Speaking of that wire, would it be okay to just leave it off?

I have a replacement MAF that I'm going to install this weekend. As long as I'm in there again, I'll take another look at that temperature sender.

You need that sensor in place and connected to get the engine to start. Not ok to leave it off.

MAF is needed too and it can cause massive over fuelling if its faulty.

Point-Seven-five · 20 Re: 1989 K100RS SE Won't Start Wed Feb 26, 2020 10:30 am

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Olaf, it was the wire that locks the connector on the sender I was referring to leaving off, not the connector.

I am replacing the MAF because the one that is there now had wonky resistance readings. I opened it up and got the wiper running on a virgin part of the element, but I just don't trust it. BTW, correcting the wonky resistance readings still didn't correct the overrich fueling condition.

92KK 84WW Olaf · 21 Re: 1989 K100RS SE Won't Start Wed Feb 26, 2020 12:06 pm

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The reason I am so interested in this one is my 84 K100RT is doing the same thing and essentially the same bike. I have done all these things you have done including swapping out ICU and FICU with known good spares to no effect and I was back at it about 2 weeks ago. It isn't an urgency for me because I use the the K100RS and K1100LT all the time but my RS is going to Spain next week and being left there so I have to get this sorted.

Briefly, the things I have not done.....

Change MAF, which my ex BMW guru friend says is top of the list for being the cause [have one on my shelf].
Change fuel pressure regulator [have a new one on my shelf] as apparently these can have hidden problems.
Noticed about 3 weeks ago a vacuum pipe issue into fuel pressure regulator, new pipe needed.

Point-Seven-five · 22 Re: 1989 K100RS SE Won't Start Wed Feb 26, 2020 12:26 pm

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Olaf, like you this is my third bike and there is no real urgency to getting it running. I bought it knowing it didn't run and the previous owner had given up on it. I have lots of time as there is still at least two months until riding season. As a matter of fact, we're looking at about a foot of snow between now and the weekend.

The garage is pretty cold so my wrench sessions are pretty short. As I write I'm working up the ambition to go out there and fire it up to see which cylinders are not firing.

It is disturbing to hear that the ECU and ICU didn't solve your problem. I keep thinking that is where my problem is, and they aren't cheap just to swap out for the original to confirm the cause.

Laitch · 23 Re: 1989 K100RS SE Won't Start Wed Feb 26, 2020 1:00 pm

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Point-Seven-five wrote:It is disturbing to hear that the ECU and ICU didn't solve your problem. I keep thinking that is where my problem is, and they aren't cheap just to swap out for the original to confirm the cause.

Read to the conclusion of this thread.

Point-Seven-five · 24 Re: 1989 K100RS SE Won't Start Wed Feb 26, 2020 1:48 pm

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Laitch, I remember seeing that thread when I was searching for information. I didn't think the Hall Sensors were applicable to my situation because I had spark on all cylinders, and the injectors were pulsing. I think you have added another item to my list of things to check.

I did get out to the garage this afternoon and took some readings followed by an attempt to start the bike.

First, the ambient in the garage was a balmy 42F/6C. The water temperature sensor resistance was measured from pin #10 to the frame ground. Reading was 4.93K ohms which is perfect according to the chart in Bert's troubleshooting guide.

I rechecked the MAF and the readings here were the worst I've seen. I'm thinking it is beyond hope. Pin 7 to 5 was 80 ohms which is good according to Bert, but all the others were way out of spec.

So I tried to start the bike. The plugs were the "old" ones that I cleaned because I didn't want to ruin the new ones. The engine started after a couple seconds of cranking. Checking exhaust outlet temperatures, the engine was only running on cylinder #4.

After about a minute of burping and farting cylinder #1 decided to start firing followed about another minute later by cylinders #2 and #3. Once they were all firing properly, the throttle response gradually improved and the engine would idle. Altogether, it took about 3-4 minutes from first start to finally running. Turned it off, and then tried to restart. Engine started immediately.

This is essentially what I have been dealing with all along. I expect that if I let it sit until totally cold again, it will not start unless I clean the soot from the plugs.

I think I'll check the MAF resistance again.

Stay tuned.

92KK 84WW Olaf · 25 Re: 1989 K100RS SE Won't Start Wed Feb 26, 2020 1:55 pm

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What sort of gas is in the tank..........just curious......

Did you use the 'choke' for the first start up?
Did bike need choke for first start up?
Is it possible the fuel pump is slow to build up fuel pressure.....potential FPR/diaphragm issue? Fuel pump to FPR should be I think 60 psi and 36 psi after FPR.

Laitch · 26 Re: 1989 K100RS SE Won't Start Wed Feb 26, 2020 2:17 pm

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Point-Seven-five wrote:Stay tuned.

You bet! I try not to miss an episode.

Point-Seven-five · 27 Re: 1989 K100RS SE Won't Start Wed Feb 26, 2020 2:19 pm

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92KK 84WW Olaf wrote:What sort of gas is in the tank..........just curious......

Did you use the 'choke' for the first start up?
Did bike need choke for first start up?
Is it possible the fuel pump is slow to build up fuel pressure.....potential FPR/diaphragm issue? Fuel pump to FPR should be I think 60 psi and 36 psi after FPR.

Fuel is corn free premium, less than two weeks old.

Choke at position one, as soon as engine fired I had to open the throttle to keep it running.

Fuel pump and regulator are working properly. Pressure jumps almost instantly to 40psi and quickly drops to 36psi where it sits steady. After the engine is shut down, the pressure takes several minutes to drop to 0psi indicating that the regulator diaphragm is flexible and the outlet orifice is clean.

Point-Seven-five · 28 Re: 1989 K100RS SE Won't Start Wed Feb 26, 2020 2:22 pm

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Going on hold for a couple days while I wait for the weather to warm up a bit.

Next step is to swap MAF sensors and check the Hall Effect thingies.

volador · 29 Re: 1989 K100RS SE Won't Start Wed Feb 26, 2020 2:34 pm

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What type spark plug wires are you using?

5KΩ or air gap type?

92KK 84WW Olaf · 30 Re: 1989 K100RS SE Won't Start Wed Feb 26, 2020 2:41 pm

92KK 84WW Olaf

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Plugs will not have an R in the code, eg NGK D7EA and will have bobbins on.

Did you get new injectors or refurbish the originals single hole injectors?

Point-Seven-five · 31 Re: 1989 K100RS SE Won't Start Wed Feb 26, 2020 2:47 pm

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volador wrote:What type spark plug wires are you using?

5KΩ or air gap type?

OEM wires that measure 5k ohm from Coil connection to the center electrode with the spark plug plugged in.

Plugs show 0 ohms from terminal to center electrode. All plugs have official NGK terminal nuts.

Point-Seven-five · 32 Re: 1989 K100RS SE Won't Start Wed Feb 26, 2020 2:55 pm

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92KK 84WW Olaf wrote:Plugs will not have an R in the code, eg NGK D7EA and will have bobbins on.

Did you get new injectors or refurbish the originals single hole injectors?

New "direct replacement" single hole injectors. One troubling thing that is nagging in the back of my mind is that their coils are 12.8 ohms instead of the 16 ohms of the originals. Still, according to the seller, they flow the correct amount of fuel(14#/hr) and he has sold several sets with no problem.

The seller has a 99.3% rating at ebay and no bad reviews on the injectors.

The engine seems to run fine if a little rich once it gets going, and when I first put them in, the bike ran really well on my test rides.

92KK 84WW Olaf · 33 Re: 1989 K100RS SE Won't Start Wed Feb 26, 2020 3:05 pm

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When the resistance changes the flow rate changes but the flow rate is also given at a certain fuel pressure, you would need to know that too.

I put brand new 4 hole 16v injectors in the RT as a temporary measure for about 3,000 miles, consumption increased by about 15% but it ran very clean.

Is that flow rate 14 litres per hour? As in 233cc per minute? Seems high to me BUT you still need choke to start too?

MartinW · 34 Re: 1989 K100RS SE Won't Start Wed Feb 26, 2020 4:43 pm

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Point Seven Five wrote:
So I tried to start the bike. The plugs were the "old" ones that I cleaned because I didn't want to ruin the new ones. The engine started after a couple seconds of cranking. Checking exhaust outlet temperatures, the engine was only running on cylinder #4.

After about a minute of burping and farting cylinder #1 decided to start firing followed about another minute later by cylinders #2 and #3. Once they were all firing properly, the throttle response gradually improved and the engine would idle. Altogether, it took about 3-4 minutes from first start to finally running. Turned it off, and then tried to restart. Engine started immediately.

This is essentially what I have been dealing with all along. I expect that if I let it sit until totally cold again, it will not start unless I clean the soot from the plugs.

You need to determine whether have a good spark on all four cylinders initially on start up.
Regards Martin.

mike d · 35 Re: 1989 K100RS SE Won't Start Wed Feb 26, 2020 5:18 pm

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I agree with checking for sparks at fist start up, but at 6C I would be using full 'choke' - admittedly this is on my K1100 and assumes the replacement injectors are providing a similar flowrate as OEM ones.

Mike

Point-Seven-five · 36 Re: 1989 K100RS SE Won't Start Thu Feb 27, 2020 12:53 pm

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Olaf, the flow rate is 14 pounds not liters per hour. This number matches the Bosch spec for the OEM injectors. The Bosch flow spec is at 3 bar, while the bike runs at 2.5 bar. At that pressure the flow is specified at 12.85 pounds/hour. From what I read on injector sites, even though the K bikes run at 2.5 bar, the standard pressure for flow rate specs is 3 bar.

Martin, I get a good blue spark on all cylinders with the used plugs out of the engine.

Dead in the water right now. Temperature in garage is 16F. Won't be warm out there before Sunday. Only thing I might do is change the MAF. All the wonky readings I am getting from it has pretty much destroyed any faith in it working even close to properly. Might do a quick test on the Hall Effect Sensors by heating them a bit with a hair dryer. No ambition to do much more. Besides, I have some boat parts I need to get ready.

MartinW · 37 Re: 1989 K100RS SE Won't Start Thu Feb 27, 2020 2:13 pm

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After it starts on one cylinder shut it down and check the plugs, are they wet or dry?
Regards Martin.

Point-Seven-five · 38 Re: 1989 K100RS SE Won't Start Thu Feb 27, 2020 8:17 pm

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Wet.

daveyson · 39 No go Thu Feb 27, 2020 9:18 pm

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The problem might go away if you replace the injectors. The resistance is too low, when the wire gets hot, the resistance increases. Maybe

MartinW · 40 Re: 1989 K100RS SE Won't Start Thu Feb 27, 2020 9:33 pm

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What does it do when you press the start button when idling at 1000 Rpm?
Regards Martin.

volador · 41 Re: 1989 K100RS SE Won't Start Fri Feb 28, 2020 10:46 am

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MartinW wrote:What does it do when you press the start button when idling at 1000 Rpm?
Regards Martin.

LE Jetronic training reference pg.18
Note:With the engine running (>700RPM) additional enrichment can be achieved by holding down the start button. The fuel injection control unit perceives this as a start signal and initiates additional enrichment. The ignition control unit will not activate the starter relay with the presence of TD > 700 RPM.
TD-Processed Engine Speed Signal

92KK 84WW Olaf · 42 Re: 1989 K100RS SE Won't Start Fri Feb 28, 2020 11:28 am

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New "direct replacement" single hole injectors. One troubling thing that is nagging in the back of my mind is that their coils are 12.8 ohms instead of the 16 ohms of the originals. Still, according to the seller, they flow the correct amount of fuel(14#/hr) and he has sold several sets with no problem.

Thats in the back of my mind.

Another member here, Charlie Bashford, like myself has an interest in music systems. When we look at speakers and wattages 80W at 8 ohm I think gives you 160W at 4 ohm. If the same rule applies to the injectors then you maybe end up delivering 25% more fuel...

The fact that it affects all 4 cylinders is pointing to something that either controls all 4 or is common to all 4.

Point-Seven-five · 43 Re: 1989 K100RS SE Won't Start Fri Feb 28, 2020 12:02 pm

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Olaf, I started building PA systems for bands around 1965 when I was still in high school. Amps, mixers, and speaker cabinets from scratch. I learned electronics from the RCA Receiving Tube Manual.

I don't think an injector is the same as a speaker. Whereas a speaker is linear, I am pretty sure an injector is a binary device.

Ohm's law says the lower impedance injector will draw more current, creating more power to move the pintle. The fuel flow rate at full open will be the same regardless of impedance, where the difference is is in the opening force available, and the resulting response time reduction. Assuming the return spring's rate is the same, there is probably just a few microseconds difference in the opening time. I suspect that response time has virtually no effect on the amount of fuel delivered. However, the higher force means more drive to power through internal deposits in the injector.

I have no idea what the Q of the coil is or how it affects the response or fuel flow. Again, if the hourly rate is the same, I suspect the effect is nil. Electrically speaking, injectors are operated at pretty low frequencies.

My concern with the lower impedance is the effect of the increased current flow on the switching transistors in the ECU. More current = More heat. As anyone who rides these beasts knows, there is lots of heat already. Can the ECU handle the extra heat generated in the box? That is the real question to me.

As long as they are installed as a set all cylinders should see essentially the same fuel delivery and operate the same. It might be a different story if they were mixed with 16 ohm OEM injectors.

92KK 84WW Olaf · 44 Re: 1989 K100RS SE Won't Start Fri Feb 28, 2020 12:27 pm

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Number of posts : 7955

Nicely explained too! I just don't go into the electronics much....I left that to my brother who introduced me to these systems...especially Linn which I love but that's whole other story..... 2 x K = 1 Amp.

Th only thing controlled in the injector is time...they open or they don't open.

So back to MAF.......TPS FICU and ICU

Laitch · 45 Re: 1989 K100RS SE Won't Start Fri Feb 28, 2020 12:58 pm

Laitch

Life time member

Number of posts : 3253

volador wrote:LE Jetronic training reference pg.18
Note:With the engine running (>700RPM) additional enrichment can be achieved by holding down the start button.

Do you have a reference name and publisher for that manual? Inge seemed to have a different opinion

Point-Seven-five · 46 Re: 1989 K100RS SE Won't Start Fri Feb 28, 2020 1:09 pm

Point-Seven-five

Life time member

Number of posts : 4217

Once the garage gets a bit warmer I'm going to go back out and check everything one more time. Probably Monday.

Especially interested in the Hall Sensors, the MAF, and the TPS. I need to confirm the Hall Sensors are working when cold, and the MAF and the TPS are giving me wonky readings. Going to swap out the old MAF for one I just bought.

Laitch · 47 Re: 1989 K100RS SE Won't Start Fri Feb 28, 2020 1:19 pm

Laitch

Life time member

Number of posts : 3253

Point-Seven-five wrote:Once the garage gets a bit warmer . . .

I've warmed up by shoveling snow all morning. Laughing

The shop should feel comfortable enough to work in for a while but I'm not done shoveling yet. Laughing

Point-Seven-five · 48 Re: 1989 K100RS SE Won't Start Fri Feb 28, 2020 1:44 pm

Point-Seven-five

Life time member

Number of posts : 4217

I'm going to dig out in about 15 minutes. Only have about 6 inches out there, but the wind is still at 25-30mph. Got tired of waiting for it to stop. Just glad we didn't get the two feet the hysterical weather people were forecasting.

volador · 49 Re: 1989 K100RS SE Won't Start Fri Feb 28, 2020 3:27 pm

volador

Platinum member

Number of posts : 268

Laitch wrote:

volador wrote:LE Jetronic training reference pg.18
Note:With the engine running (>700RPM) additional enrichment can be achieved by holding down the start button.

Do you have a reference name and publisher for that manual? Inge seemed to have a different opinion

Level 2: LE Jetronic Training Reference Book
BMW of North America Inc. Motorcycle Training 1993 or 9/99

1993 pg16 version stated (>500RPM) 1999 pg18 stated (>700RPM)

Inge was the authority I'm the messenger of what I have read briefly in front of me.
Bought the binder on Ebay, when able I will scan and upload.

MartinW · 50 Re: 1989 K100RS SE Won't Start Fri Feb 28, 2020 4:43 pm

MartinW

Life time member

Number of posts : 3012

I've been told the 711 Rpm figure but I don't know if K75's are different but my starter will engage under 1000 Rpm. scratch

I've got a couple of mates with K100's coming over today if I remember I'll try them.
Regards Martin.

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