Linky: http://classickbikes.com/ckb.tech/0.ckb.tech.files/k11tbk75/k11tbk75.htm

This is what we like. I'm interested to hear how the installation and end result goes. I reckon the quite under-stressed K75 motors have a fair bit of extra hidden within which mods like this tap into.

Thanks for the link.

Duck you are always coming up with creative ideas. 

I am still awaiting my starter brushes, they must have to be made in Germany then shipped over or something like that, then I can try to start my RS, now RT!

Creative ideas?  All I did was copy what somebody else had done.

The last creative thought I had was in 1972.

I have been thinking of doing that and putting a motronic on it.

I fired up the K75 today after completing my customization, first time in 1.5 years.  I fitted some K1100 TBs as part of the customization. Read about the installation of these on my blog

The motor started but ran roughly for a K75.  I put the Carbtune on the TBs and sure enough, the TB sync is out of whack.  Cylinder 1 is pulling about 34 cmHg, Cylinder 2 about 24 cmHg but Cylinder 3 is zero cmHg.

I'm not sure what to make of this.  Here's what's been done:

• K1100 TB put in place of the K75's.
  
• all air bypass screws reset to 1.5 turns out
  
• TB bushings between engine and TB and TB, and air plenum were all checked for deterioration;  they appear in good condition.
  
• brand new rubber caps sealing off the balance tube inputs at the back of the TBs
  
• RTV used between TB bushings and intake manifolds to seal
  
• "Z" tube between air plenum and engine is brand new; no cracks or splits.
  

Can anyone suggest why the Cylinder 3 TB doesn't pull any vacuum?  This was the TB that I replaced the pivot shaft so there is the possibility that the butterfly valve is maladjusted but I wouldn't expect zero vacuum.

I think that the only cause of this is air leakage but where? I'll try the propane trick to confirm this.  Should this be my next troubleshooting step or something else?

You didn't mess the silver screws between the TBs, did you? Perhaps the vacuum tube on #3 is clogged.  I'd try cleaning it out with a piece of wire down the brass vacuum tube.

BTW: The other day I measured the intake port on a K75 cyl head.  31mm so I'm not sure if this mod would make a material difference.

I didn't touch the Sacred Screws at all.  Paint is intact on them so the K1100 PO didn't mess with them either.

I'm fairly certain that the air ports were clean.  The TB assembly was pretty cruddy when I received it in the post so I thoroughly cleaned them with carb cleaner and WD40.  I remember checking all the holes but I may have missed something.

If air is being pulled through some other part of the TB, will vacuum show up as zero on the manometer?  After thinking about this for a while, I'm suspecting the K75 pivot shaft, because that is the only part I've changed on the entire assembly. Maybe the rubber shaft o-rings are not sealing properly and air at idle is being drawn from around the pivot shaft on Cylinder 3 TB.

duck wrote:BTW: The other day I measured the intake port on a K75 cyl head.  31mm so I'm not sure if this mod would make a material difference.

Is the intake port on a K100 larger then?  In the other thread, those who have done the mod on a K100 rave about the change in characteristics of the bike.  That's where I misread the 3mm different in port size; I must have thought that up myself.  You're right in your measurements, the butterfly valves are within 1mm of each other.

Do you get any vacuum if you rev it up? What did you put on the port on the back of it?

duck wrote:Do you get any vacuum if you rev it up? What did you put on the port on the back of it?

No, no vacuum.   In fact, vacuum drops in all cylinders towards zero as revs increase.

I sealed up the back ports with rubber caps (1/4" if I recall).  These caps are visible in the pictures on the blog.

sounds like that port structure either side of the butterfly is blocked rob
(or something is holding open the valves )

can you spray some carbi cleaner through the port top to bottom  or did you check before assembly ?

inlet port size on the k100 looks to be 31.76 mm at the face of the head .

Compression test just to be sure, before digging in to anything major.

I'll do a compression test later this week.  I hope I haven't got ring problems because there was nothing to indicate taht before I began my teardown a year and a half ago.

I sprayed carb cleaner around the area I suspected, TB3 pivot shaft.  I used one of those straws in the spray can to make sure that the area could be precisely isolated.  I found that the idle RPMs consistently rose slightly when I sprayed around the shaft where it exited to the TPS switch.  Seems that the seal is failing in that area and I'll have to tear off the TBs to examine them.

I will also do a thorough recleaning of the TBs while they are off to make sure all the ports are clear.

I was reading some earlier posts about TB syncing and Themason emphasizes pinching off the vacuum hose that goes to the fuel pressure regulator when doing the resync.  I didn't do that.  It may have an effect but I'll recheck later this week.

Thanks very much for the suggestions.

People say it's best to get a T style connection for syncing the vacuum on the first TB.  That way the FPR vacuum hose can still be connected while you set the vacuum on the TB.  In my opinion, it's just important to have a consistency throughout the entire process.

I just disconnected the FPR vacuum hose from the first TB when I did my sync, then plugged the 1st TB with a rubber cap, synced all the TBs with the hose still disconnected, then reattached it.

It is possible it could make a difference when reattached.  You'll just have to listen to the possible difference in idle.  Obviously, this isn't the greatest method for people wanting a super well tuned sport running bike, but my bike runs and idles pretty damn well.

This part is another topic of great debate on the forum.
I found that when I disconnected the FPR vacuum hose, the bike idled smoother and wasn't as luggy in the low end.  Much smoother and easier to ride at slow speeds in 1st / 2nd gear.  It didn't stutter as much in idle, and was a much more consistent powerband throughout the RPMs.  I haven't noticed a loss in mileage, or any negative side effects.  My FPR was brand new when I put it in a little under a year ago.  Just something to think about.  (I have the 1992 k100rs, 16v, with the MOTRONIC injection system, but I believe others have had similar results with the L-Jetronic system.)

This part is another topic of great debate on the forum.
I found that when I disconnected the FPR vacuum hose, the bike idled smoother and wasn't as luggy in the low end.  Much smoother and easier to ride at slow speeds in 1st / 2nd gear.  It didn't stutter as much in idle, and was a much more consistent powerband throughout the RPMs.  I haven't noticed a loss in mileage, or any negative side effects.  My FPR was brand new when I put it in a little under a year ago.  Just something to think about.  (I have the 1992 k100rs, 16v, with the M OTRONIC injection system, but I believe others have had similar results with the L-Jetronic system.)




interresting that the milage didnt go down ,since this mod should raise the fuel pressure a litlle at the injectors




k-rider

Last night I had time to remove the TB assembly from the K75 and inspect it.  This is what I discovered.

1.  The butterfly valves were not positioned correctly relative to each other and consequently, had different degrees of open-ness.  The butterfly valve on TB1 was almost sealing up the throat of the TB; the gap was a little larger on TB2; and TB3 was open the most, revealing almost 0.2mm of space between the valve and the TB throat.  These differences correspond with the vacuum readings I was getting.  When reassembling the TB, I took extra care in positioning the butterfly valve, more care than I observed originally.  I made sure that the valve would very precisely fit the TB throat. When I had the TB assembly back together, I did the forbidden and adjusted the interlink screw between TB2 and TB3 to close up the valve opening in TB3 and make it equal to that opening I observed in TB1.

2. Air was leaking in through the pivot shaft at the TPS because of excessive lateral play in the shaft.  When I removed the butterfly valve from TB3, I could move the shaft back and forth almost 2mm.  I compared this play to the play in the K1100 TB I removed originally and there needs only to be a fraction of a mm play.  I then compared the pivot shaft from the K1100 TB and also from the original K75 TB.  I discovered that the cir clips were in different relative positions.  The K75 cir clip is positioned nearly 2mm further along the shaft than the K1100.  This difference accounts for the width of a rubber washer (there is only one rubber washer that seals the shaft at one end of the K1100 TB but two washers that seal each end on the K75 TB).  I added two 1mm thick washers to the shaft to take up the slack and eliminate the lateral play in the shaft.



3.  I spent some time cleaning all three TBs again.  This time I used a pipe cleaner and acetone to clean the bores of the various inlet ports.  I made absolutely sure that they were clean of all residue and fully open.

I'm ready to reattach the TB assembly and try to sync them again.  With the base adjustment of TB3 set, I expect the Carbtune readings to be closer together.  From this point, I'll fine-tune the interlink screws and then set the air bypass screws, as outlined in Rob Lentini's process.  Hopefully, I've solved the air leakage problem as well.

good find rob


I had to redo the throttle bodies on the k100 recently ...ones that were unfamiliar to me (from someone else ) ...I couldn't find a happy position for an idle that was smooth, as some one had adjusted the 2 to 3 linkage at some point in the past ..
I chose to alter the linkages manually without some reference gauges and roughly altered by ear and feel of the bike under acceleration and deceleration ...  additionally I had visually noticed some lag on idle up - choke tb positions between the inner and outer bodies ..( I guess as they age some slight movement occurs ..although not apparent how that happens, wear I guess  ) which I left alone at that time .

after the bottom end rebuild, albys fantastic carb sticks helped me settle that observed lag of the outer tbs ,to something way better , by adjusting the apparent laggy ones to now unnoticeable differences ...the bike now rides and idles like a champ and very consistent closure at all occasions to idle like a new one .


best to open the bypass screws to 1 turn only on each, then attach the carbtunes and take the throttle to about 3k  and notice the vacuum changes as it accelerates and decelerates to that .

make suitable adjustments on the linkages so that they all sync a bit better as the revs increase and the vacuum decreases  ..you will get a feel for it as you make adjustments I guess .

alternatively as others have posted previously,  the use of a drill bit or several of the same size , could help establish an opening synchronisation in relation to the butterflies.

just make sure that the bypass passages, needle and seats are impeccably clean before hand .
I have noted on several occasions that a fair amount of carbon build up (possibly from blowback from the inlets valves and induction of breather tube vapours etc )  do seem to coat the passages and needles with some particularly tough to remove coating of crap ( a good solvent and an overnight soak often helps remove it, along with pipe cleaners and acetone  ) .

all the usual disclaimers apply ...like getting the clearances for the valves correct before starting , rubber injector seals all sorted and tb rubbers top and bottom repaired ..sealed properly along with good needle valve seal rubbers .

after adjustment then set the idle synchronization from the initial "1 turn pre-set" and idle screw on the choke lift bar ...they should line up to a very similar position of turns out .

Sorted!!

The K1100 throttle bodies are fully synched and functional on my K75.

I reattached them and the bike fired up but still ran rough.  Some debugging showed up a failing injector in cylinder #1.  Replaced that and she ran.  

I loosened the inter-body lock nuts, put the Carbtune on the vacuum ports, fired up the engine and screwed in the air bypass screws until seated.  I used the fast idle cam to maintain 1500RPM.  The initial reading showed imbalance with cylinder #1 drawing significantly more vacuum than the other two.  I carefully adjusted the inter-body screws to get balance between the three readings and succeeded.  Below is a photo of the best balance I could achieve over the RPM range 1200 - 2500:



I locked the settings at this point.  Once that was done, I unscrewed the three air bypass screws to one turn each and took off the fast idle because it was no longer necessary.  A couple of small adjustments on TB3 brought sync to the assembly at idle:



Idle is rock steady.  Went for a ride and the "butt-dyno" indicates more apparent torque in the low revs and apparent HP in the mid and high ranges.  I have no empirical data to support this claim; it could just be euphoria at finally getting the stuff to work.

Signed -- One Happy Camper!

If a 'sense' of something is enough I'd say you DO have empirical evidence! Congrats on getting 'er sorted. Sometimes we just have to rehash things, take a coupla steps back to move forward.
 

hooray !!!

ride well rob

can i see a cheezy grin over there  ?

robmack wrote:I fired up the K75 today after completing my customization, first time in 1.5 years.  I fitted some K1100 TBs as part of the customization. Read about the installation of these on my blog

So I am prepping parts for this K1100 throttle body swap to my new / old K75, after reading all three blog threads on it.

So far, I bought a NASTEE(!) K1100LT throttle body assembly off FleaBay for $43, and just spent Saturday bathing its components. I first used carb cleaner (meh...) and then went with someone's suggestion from another thread and used a mix of 2 liters of Dawn dish soap + 2 liters of coffee-temperature white vinegar.

I poured everything together this morning into a small Target plastic covered storage tub, and every hour I inverted and shook up the contents. This evening, I tooth-brushed all the pieces off, pipe-cleaned all orifices, hot-washed everything several times in the sink, and hung them up to air dry through tomorrow.

I have to say that I am impressed. The hot vinegar + Dawn witches' brew loosened all the grime in several hours. Several parts look brand new and the others, almost so.

Despite this soaky-washy treatment, the four "Sacred Screws" haven't moved and their factory blue paint is still in place.

I bought another cheapo used throttle body assembly, this time from a K75, so that I can swap the butterfly shaft off the TPS-actuating end throttle body without shutting down my K75 until the actual transplant day.

I am also toying with half-shafting the throttle body shafts & screws while this is all accessible. In for a penny, in for a pound, right?

To be continued... comments and suggestions are most welcome.

What is the merit of putting K4v throttle bodies on K2v?

Poupy wrote:What is the merit of putting K4v throttle bodies on K2v?

The opening link of this thread is a dead link but here is a link to the source that was described as its original inspiration.
http://k75retro.blogspot.com/2014/04/adapting-k1100-throttle-bodies.html

Yes, I had read that document, which is for me a discovery, though I think I have already read a lot of litterature about ks modifications.

In my opinion, whatever you do to the inlet pipe, the bottleneck is the intake valve, smaller anyway.

I consider that the bmw's conceptors knew their job and that what they got from the k2v engines was/is the maximum they could. To get more, they had to play with the cylinders head, adding valves and modifying other details, which lead to the K1 and K100RS/1 engines. Still with paper type air filters...

In the document I surprisingly find no trace of throttle rail synchronisation procedure.

I read here and there in this group about "sacred screws" on the throttle bodies which should not be touched under any reason. I find it strange. How then do you achieve the throttles synchro, using a Carbtune or equivalent. Just by playing with the brass screws?
I have dismantled throttle bodies rails to study how they are designed and I must confess that if there is one screw which should never be touched, it is the one wrongly called "of idle speed adjustement", in the middle of the ramp. The other 3, between throttle bodies can be touched, but not anyhow. A logic approach is necessary.

If you are interested, we can compare our convictions

Poupy wrote:I read here and there in this group about "sacred screws" on the throttle bodies which should not be touched under any reason.

If you are interested, we can compare our convictions

When it comes to mechanical encounters, my convictions are adaptable based on preponderance of evidence.

As far as sacred screws . . . which should not be touched under any reason are concerned, you seemed to have missed the thread containing this post.

Ok, not everybody says that those sacred screws should not be touched. Reassuring news.

This being said, when reading through the subject that you mention, the certainty of starting at the good starting point is generally questionned. And apparently, when wishing to make a synchro, everybody's first gesture is to plug the Carbtune on vaccum plugs and start the engine.

I am convinced that it is too fast. For me, if a synchro is bad, the thing to do is to demolish it and make a brand new one, starting from scrap. This is why:

This is a K100 throttles assembly, direct from my barn. It is under no constraint, its sacred screws have been completely removed. The central "idle regime" screw is unscrewed as well.

For adjusting it - on the bike, no need to dismantle it - the TPS must be freed (or removed), as well as the gas and choke cables.


Clicking on the image to see better, it is noticeable that the throttles openings tend to be more and more important when moving from left to right, i.e. from the bike front to back.

That, in itself, is somehow strange because once the throttles are separated from their holding rail, the first three are very similar, all of them fitted with a return spring bringing them in closed position which, even free, is not what appears on the image.The fourth throttle has no such spring. 

Here they are, separated from their rail, except the last one, shown wide opened:


The spring, when present, completely closes its throttle, by pulling down its RH side lever. The first throttle has only one lever, on its right side. The last throttle, without spring, has also only one lever, on its left side. The central throttles have a lever each side.
On K1100, for a non obvious reason, the third throttle assembly has no spring. Maybe because of the K1100 gas handle design which would have made the necessary opening effort uncomfortable against 3 springs.

Anyway, now comes the interesting bit: the junction between throttle 1 and throttle 2

Sorry for the orientation upside down, I was looking for light

On those images they are just next to each other, both of them closed by their own sping. The junction assembly between them is extremely slack, with a gap of about 4 mm between the respective levers. That gap is supposed to be filled by the first adjustment screw, keeping in mind that:
- the opening instruction comes from the gas cable, i.e. from the right for the first two throttles.
- the RH levers can only move upwards, as in the other direction the throttle is blocked against the tubular body. Tightening a screw too much opens all the throttles located on its left.

That is the level of the first throttle RH lever when that throttle is in sure closed position (on this image it would be the same if the screw were absent):

And that is the same lever position when the screw has been screwed to its maximum:

That means that the good time to stop joining the two together is when the first throttle RH lever begins to raise. If it raises you went too far.
Once that optimal relative position has been found, the counternut can be tightened.

Same operation for the screw between throttles 2 and 3. Make sure that the central wrongly called "idle speed adjustment screw" is far from its contact plate. When ajusting the second "sacred screw" check that the RH lever of the FIRST throttle does not move up. If it does you have gone too far. The purpose of the game is making sure that all the throttles are well closed together, the reference one being the first one. Here again, once the correct adjustment screw position has been found, the counternut can be tightened.

Once the junction between throttles 2 and 3 has been achieved, it is time to put the central "idle spleed" screw just against its plate. The purpose of that screw is to prevent the throttles to act as stop pieces when the ramp arrives in closed position. Steel against steel is more resistant than brass against aluminium!

Finish with the adjustment of the junction between throttles 3 and 4, still making sure that the RH lever of the FIRST throttle does not move up. Once more, tighten the counternut when it is finished.

That is it. You have spent 10 minutes and are then on a sure correct basis. It is then time to reconnect the gas and choke cables and to play with the Carbtune for the final fine tuning. If it goes beyond control, redo from start.

At the very end, adjust the TPS. And then, when you tell the Jetronic or Motronic that the throttles are in closed position, they are, which implies calculations on solid basis.