Hi all

Short one:D . Is there a mmHg value for the TB sync, or should the columns just be aligned at idle speed? Also which cylinder is reference, no1 or no4 where the TPS is mounted. I´m using a carbtune pro for sync.

16V model, dont know if it makes a diff?

Regards

Bjarne

hi bjarne try either 2 or 3 ...they are closest to the cable - linkage centre and would be least out of calibration since factory setup of the assembly...many years ago now

Columns should be aligned since synching is a relative adjustment, not an absolute adjustment.

Follow the wisdom from the Kguru, Rob Lentini:

I don't do anything with cylinder 4 and use this as my base to set the others by. I have found when setting the TBs that when you adjust one it changes the others. That is why I feel it is important to have a 4 gauge meter so you can see how the adjustments change the other TBs. I use a Carbtune and it works great with no nasty mercury.

There are 3 inter TB adjusters only!
1 between cyls 1 and 2
1 between cyls 2 and 3
1 between cyls 3 and 4.

start with 1and2,
then do 3and4
then do 2and3

HTH

robmack wrote:There are 3 inter TB adjusters only!
1 between cyls 1 and 2
1 between cyls 2 and 3
1 between cyls 3 and 4.

I`ll guess threadstarter intend to adjust the throttle butterfly bypass screws, rather than the linkage
(which normally shouldn`t be disturbed, unless a flow bench is available).

Inge K.

Inge K. wrote:

I`ll guess threadstarter intend to adjust the throttle butterfly bypass screws, rather than the linkage
(which normally shouldn`t be disturbed, unless a flow bench is available).

Inge K.

So what vacuum level should one expect at the throttle bypass?

don `t do anything before the complete rubber stuff is new

All 4 cyl models:
cylinder 3 is the reference !

succession
first: cylinder 2
second: cylinder 1
thrd: cylinder 4

http://www.ziegeltreiber.de/images/d/db/KarachoI.pdf


All 3 cylinder models:
cylinder 2 is reference !

Agerbundsen wrote:So what vacuum level should one expect at the throttle bypass?

It isn`t any specific value for this, since it`s much different things that affect this value.

And it can vary on the same bike over time as this and that are worn, and different maintenance
tasks is done, what is important is that all four cylinders is adjusted to the equal value.

But by memory I usually end up somewhere around -0,4 bar at idle, others in here might have
other experience about this.

Inge K.

In my tests/adjustments on an old 2V K100rs, I found that I could balance cylenders 1,2 & 3 at approx 10" Hg.

#4 however seems to be consitantly low reading only about 1/2 the others and the bypass air adjusting screw seems to have little or no effect in the readings. It does not appear that anyone has tried to make any adjustments on the linkage screws.

I did try moving the linkage screw in & out on number 4 only, paying close attention to getting it reset back to it's original position. No amount of fiddling in either direction improved the reading at the gauge port, (I have checked & rechecked the valve clearances and have all new rubber boots & manifolds, including a new breather hose. The system has been checked & rechecked for air leaks, none found.

I find it curious that #4 is low even with the air bleed screw seated fully closed. On all the others, closing the screw raises the vacuum reading, opening the screw lowers it.

My question is: With #4 being consstantly lower than normal, would that cause the FPR to create more pressure at idle than would normally called for? What do you think about moving the FPR vacuum line to #3 since the vacuum there seems to me more "in spec"?

Can I assume that because #4 is low and unresposive to adjustments.... that I probably have a defective intake valve on that hole?

I have yet to get a 12mm adaptor for my compression gauge so I can not test compression at this time.

Inge K. wrote:

Agerbundsen wrote:So what vacuum level should one expect at the throttle bypass?

It isn`t any specific value for this, since it`s much different things that affect this value.

And it can vary on the same bike over time as this and that are worn, and different maintenance
tasks is done, what is important is that all four cylinders is adjusted to the equal value.

But by memory I usually end up somewhere around -0,4 bar at idle, others in here might have
other experience about this.

Inge K.

ibj

heres a thought

the vacume is created between either side of the butterfly through the bypass jet assembly

one of the things that needs to be done is to clean up that path ....usually i take out the needle valve - to expose the jet that sits behind .

there is a small tube that runs from the inlet side of the butterfly to that jet ....i usually spray carb cleaner to remove the gunk that could build up there .

this is because the oil breather enters the plenum closest to the number 4 inlet stack and from what i have noticed nearly all 2 valve k bikes have a good amount of oil residue down that intake path . it might take a removal of the plenum again ...shudder ...after all that good work to clean that port up .

just for all the folks attempting to do the intake plenum and throttle body rubber replacements ... dont forget to clean up the ramstack tube that supplies number 4 )and all them actually ) ...if you can its a good idea to spray some degreaser in around the bottom of the plenum and try to clean out as much junk as you can .

second thought is that maybe your butterfly has been adjusted a little (or worn on the adjustment points ) and no longer closes fully , or even has a vacume leak comming from the shaft through the throttle body axis .

dont forget that the tps fits at the end of the throttle linkages ....and could ...if adjusted incorrectly provide some resistance to that last throttle butterfly from closing fully ...over time this could have a cumulative affect of wearing the linkage ....and worst case holding the whole throttle body linkages open to some degree .

maybe you could loosen that tps and let it relax some and reconduct the test ....

but my money is a build up of oily crap through the bypass jet .

the readings you are getting are verry low indeed .

most all i have seen can get close to 18-20mg of vacume without too many worries , given that the rubbers are intact

after doing the rubbers on gerty some months ago, i was able to get a good 20-22mg vacuume accross all tbs with a nice steady idle at about 600-800 cold (without "choke")(ambient temps about 20-25 c ) which increased on heat soak to about 900 ...just about right

hope that helps some

I am confident that all the rubbers top & bottom are right.......(new). I know there is sufficient clearnce at the tps to allow the butterflys to close completely and there are no air leaks as tested all around all the likely spots with spray cleaner.

I'm happy to see someone here post the vacuum readings they have on their tests. I expect that with some more fiddling, I could obtain higher readings by closing the air bleeds further and offseting the speed drop by slightly advancing the idle stop screw. I'm not sure there is any reason to try to obtain higher readings if I can get them all equal. The bike runs really well now. There is a limit to how high I can go because the screw on #1 is also nearly all the way closed. perhaps there is still more gunk above the butterfly in that upper 1/2 of the port cutout in the side of the throttle body.

I have considered that the overall vacuum may be somewhat low due to the possability that the timing chain could be quite worn, thus allowing the overall valve timing to be a little late.

I'll report back after I rebalance tomorrow with the new coils running correctly.

hmmm last thing that comes to mind is valve clearances and actual compression .

i would be aiming for about 10 -15 at worst case ibj,

and it cant help to clean out the ports anyhow ...do them all ...would only take another 10 minutes worst case

but you didnt say if you "taped" the vacume line going to the fpr ....im guessing you didnt and just used the port anyhow ? which would be the right thing to do i recon .

finally...you did seal up the head to tb lowwer rubbers with some form of sealant didnt you ? a few folks have done the deal and then pulled it all off to do it again ...properly ...and after checking for leaks as you describe .

good luck

After installing good coils yesterday, I went back today for another stab at syncing the throttle bodies. I found that I cound not get #4 to sync as I indicated earlier.

Now I don't recommend this for the faint at heart, but I have been a professional mechanic for near 50 years and I decided to look more closely into the relationship between the acutual butterflys and their adjusting linkage.

I found that (God Forbid) although never recommended here, I needed to go into the linkage adjusters to get a good outcome.

First, I found that by slightly closing the #4 butterfly.....readjusting the last linkage screw, the vacuum on that cylinder could be brought back up to a range that was comparable to the others. Further adjustment there, allowed me to re-open the air bleed bypass screw and still maintain vacuum.

Having found relative balance, I decided to throw caution to the wind and try to reset the whole linkage.

I started by backing out the main throttle stop screw on #3 until it no longer touched its seat. Following that, I loosend all the linkage adjuster screws and backed off each until they seemed to be in a neutral load state, neither pushing the adjacent throttle arm nor pulling back on the throttle they are seated in. This requires several readjusts between #3 and the others to insure that all 4 are indeed fully closed and none of them are holding the adjacent one(s) from seating.

Once I was satisfied that all four throttles were indeed closed, I opened all 4 air bypass screws about 1 turn & started the engine. I then had to adjust the main #3 linkage screw up slightly to maintain a slow idle.

Next, I "trial & error" adjusted each linkage screw while watching the gauges to insure that each was slightly just tight enough to take any "slack" out of the linkage. Following that i tried slightly tighter or slightly looser on each, one at a time till the engine sounded smoothest and most even firing and the gauges confimed relative equality.

I now had all 4 butterflys nearly and equally fully closed relative to each other. After that, it was an easy matter to get fine tuning between the 4 by readusting the four air bypass bleed screws to obtain a fine result. Finally, about 1/4 or turn or less tighter on the main #3 stop screw to obtain the correct measured idle speed on the rev meter.

It should be noted that all the above adjustments were performed with the idle tracking TPS switch backed off so as not to restrict the free closing of the linkage. After everything was set, the lock nuts were carefully tightened on all three linkage adjusters and last the TPS was correctly adjusted for a "click" just off the idle stop.

The whole process took me about 3 hours including re-assembling the fairings.

It runs great and all 4 sync gauges read relatively the same.

I'm done.......Time to ride!

PS: My experience in general over the years has been that any thottle body with an air bypass screw can only work correctly if the butterfly valve is fully closed. All idle air being routed through the bypass air bleed screws. Over the years, I've seen many throttle bodys on automotive applications that are actually "blocked" with a perminant type sealer on the throttle housing bore to provide a perfect "seat" for the butterfly to close tightly against for a better seal.

I'm guessing that these K100 throttle bodys are designed to have the butterflys cracked slightly open at idle.

I believe that the closer to fully closed the butterflys can be at idle, the more responsive the adjustments will be at the bypass air screws.

good work there ibj .

tedious and time consuming to get it all right ...but a good result ....enjoy !

When you balance K bike TBs, do not forget how to deal with the vacuum hose from the rearmost cylinder to the fuel pressure regulator. The carb stick hose that attaches to the rearmost cylinder should have a T-fitting in it to which you attach the vacuum hose from the fuel pressure regulator. Once the engine is started and running, that vacuum hose is pinched off tight. Watch what happens to the manometer reading to the number four cylinder when you do that. You should not adjust TB balance until you have pinched off the vacuum hose to the fuel pressure regulator. BMW even has a cool little factory too for this purpose but a surgical clamp works just fine too. I think if you do this before balancing your TBs much of the above discussion will be moot.

ibjman, I have posted explanations of setting the throttle plates here and on the Flyingbrick Forum from time to time. It is straightforward to do but requires a lot of typing to repeat it. It differs from your technique and was taught to me by a fellow who built and helped test the prototypes of the original K100 and K75. If admin wants, we can make this a sticky so I don't have to re-write this periodically as the subject comes up.