i've read just about every post on this & other forums on synching the tb's and still confused

1. is baseline 1 or 1.5 turns out after bottomimg out brass screws or another # and why?

2. do i need to remove the tps and why? mine is a sensor NOT a switch so there's is no click.

3. is tb #3 the reference tb that all others are synched to? once baseline is established is tb #3 left alone or is it adjusted? which tb do you synch to which?????

4. are these parameters correct...a. none should be turned out more than 1.5 turns?

b. none should be turned out less than .5 turn?

c. there should be no more than .5 turns betw any carbs?

5. if i bottom out ALL brass screws and start bike and it runs fine WITHOUT stalling what does that indicate???

6. what's the ideal or recommended vacuum from each tb?

7. connecting a "t:" to tb #1 w/ hose to fuel pressure reg makes NO difference from my experience. why is it requited???

8. i'm using basic cheapo vacuum gauges (2) and pinching the hose to keep needle from jumping around. i can get #1, #2, #4 to synch but the reference tb #3 always off (puts out LESS vacuum). is this normal or am i doing somnething wrong???

i got them as close as possible and now the vibration at high speeds is ACCEPTABLE. notice i didn't say GONE???!!! i don't think no vibration is possible on these freakin' bikes!!!! i got out on my '83 suzuki gs1100e chain drive this afternoon and what a difference. even w/ basic super thin grips, bike is silky smooth is all gears and rpm's up to 100 mph all day long w/ NO VIBRATION. i love my k but the vibration is annoying any way you slice it or dice it!!!!

Let me begin with a disclaimer. I'm no expert. However, I've been down this road myself and do have a few observations. Can you let us know the exact model you are attempting to tune? Let's be certain we understand what we are doing. The brass screw is just an air bleed that is supposed to have some effect at tickover or at very low throttle openings. When the butterflies are open wider, the air bleed screws are essentially irrelevant. The sync of the butterfly valves themselves should have been done at the factory and not messed with since. If they have been played with, you probably need a flow bench to sync them again. Has the paint over the adjustment points been broken? When you synchronize the TBs, you are measuring vacuum. As such, things like the condition of the rings and valves matter. If you have a problem with those items, you will never see satisfactory results from your efforts to sync the TBs. It sounds to me like you have not so much faith in your instrument (the manometer). It is possible that it is not sufficiently sensitive to measure changes in the vacuum of the TBs. Finally, let me observe that if you choose to consider #3 your reference cylinder, it by definition must remain unchanged. Otherwise, how can it be a reference point?
I've never seen any reason to fret over whether #4 cylinder connected to a "T" or the hose to the fuel pressure thingee is open or sealed either. It has never made any difference in my readings.
I hope this makes some sense and helps. Good luck.

As per above - which bike? From your description I understand it to be a K100-4V or K1100.

Most of what you said is OK, but you need to start right. Ensure that there are no air leaks and that the valve clearances are correctly verified/set. This is really important if you want to get a usable set-up. Some might do a leak-down test or similar.

If the basis is right you can start the synchronisation check.

Have you got some manual with the bike? Official BMW 'Repair Manuals' are available on line which would describe the whole process in detail for your bike.

But give us a bit more info?

_ bike is '91 k100rs 4v.

_ i have the clymer manual which just says to synch them so that they all have same vacuum

_ i'm using (2) vacuum gauges so i'm syching 2 at a time. they appear to be accurate enough for this purpose.

_ i see blue paint on one of the screws but can't be sure that they have never been messed w/. for this purpose let's assume they are fine and that everythuing else is fine. i'm not looking for perfection.

i'm just trying to get the correct procedure as the clymer and what've read on the forums are slightly differrent.

WHERE/HOW DO I GET THE FACTORY SERVICE MANUAL FOR FREE?

_ my main questions are

1. is # 3 the reference tb? on my bike it's the one that the throttle cable is connected to. it has the least amount of vaccum and it dos have a brass screw that changes vacuum when turned. from my experience of synching carbs which is identical to synching tb's, there is ALWAYS a reference or at least the service manula is specific as to which gets synched to which. clymer just says adjust them all the same.

2. what is baseline after bottoming out all brass screws...... .5, 1.0, or 1.5 turns out. clymer does not address it but the forums consistently mention 1 or 1.5 turns out

3. what is the desired vaccum from all tb's? clymer & forums do not address this spec. it would be helpful to know where i need to be

4. do adjustments have to be within .5 turns of each other and none should be more than 1.5 or less than .5 turns out? clymer does not address this but i got that info from this forum.

bike has 86k miles and runs good. i've done the easy basics like all fluid changes, plugs, air filter, techron fuel inj cleaner, tps adjustment. however gas mileage sucks and vibration is annoying. i'm just trying to smooth it out and get better mileage and synching the tb's is relatively easy and have an effect on both. so far playing w/ the brass screws has made it smoother at high speeds but too early to tell if mileage has improved. i have other bikes and too many projects so i'm not interested in tearing this thing down and starting from scratch. NOT HAPPENING. one member (rick from down under) says he's done just about everything to eliminate vibration and it's STILL there. so i don't want to go down that path. just looking for a little improvement. thanks.

here are some of my observations after 2 days of playing around w/ the brass scews:

1. when i was able to get all 4 tb's in synch the idle was around 1500 rpm's. is that an indication that the butterfly linkage screws w/ blue paint have been messed w/ and are out of balance????

2. tb's 1 & 3 -and- 2 & 4 seem to be linked together as an adjustment to one affects the corresponding one. to keep the rpms to around 1150-1200 (assumes tach on bike is accurate) i can get #1, #2 and #4 to synch but the so called reference tb #3 is off always (has less vacuum). intuitively i know they should all be in synch but i'm wondering (and obviously hoping!!!) whether my specific bike is supposed to be that way???!!!

Did you do a test for air leaks first? That might throw of results.
Indeed No 3 is the one you adjust the others to as that is the one the throttle cable directly connects to.

Your numbers:

1 If in sync but too high idle I'd close all the bypass screws half a turn and sync again. You should be able to reduce the idle to 950 and sync the bodies with the bypass screws.

2 Don't know why that would happen unless you have an air leak in the No 3 rubber boot (assuming that valve clearances are OK)

The manual can be downloaded from the download page on this forum.

I would also suggest you need to replace the rubber cups on those vacuum take off points that you are not using.

Mike