I'm attempting to balance the TBs on my 85K100RT with a CarbSync and my number 4 cylinder won't adjust up or down.  The adjustment screw moves and works in and out but no adjustments are made in the level of the fluid (vacuum).  I'm wondering if I've got it hooked up wrong.  I'm removing the vacuum caps from cylinders one through three, and then removing the vacuum hose which comes from the fuel pressure regulator. to the number four vacuum port.  I hook the sync to the four TBs and leave the hose from the fuel pressure regulator unattached.  All other adjusters/adjustments work.  I even switched the sync hoses for three and four and found the same results, no adjusting number four when the screw was adjusted.  Haven't replaced the orings on the adjustment screws.

thanks for the assistance.
Roland

probably the bypass screws- jets  are ok ... but wouldnt hurt to clean them out with a blast of carbi cleaner ...I have seen the inlet side vent tube blocked before with carbon and crap  ..

you have made sure that the tappet clearances are good and not too tight ?   always do that before attempting a tune .

after the clean ....there is a possibility that the linkage is holding the butterfly slightly open

the bypass venturi is a difference type vacuume setting (either side of the butterfly )  rather than absolute

hope that helps a little  ...or what makes sense to me at least

All good possibilities charlie particularly the butterfly. To add to that scenario, the #4 TB linkage adjusting screw may have been tampered with. Its the only one accessible without removing fairing and may have been adjusted mistakenly by a PO thinking it was an idle adjustment. That screw should have some paint on it (applied in the factory) so that it's evident when it's been tampered with. If that's the case it will be difficult to get it back to factory setting. You'll need to remove the plenum.

Another possibility is that you have a bad air leak below the TB such as in the lower rubber or your #4 injector is not seated properly. O-ring may be perished.

Cheers

I'd guess leaky boot between the TB and cylinder head.

all good suggestions

Do you have a T piece connector between no 4 tb, vacuum tube and gauge setup.

I thought the "best practice" was to plug the end of the tube running to the fuel pressure regulator. No?

JMHO but what I do with my Carbtune is have a T to the FPR on the #4 hose since that's closest to what happens when riding.

+1.  I'm with the Duck on staying close to actual running conditions.

I rechecked and tweeked the balance on the K110RS TBs using the T-connector on #4 as suggested and the bike now has never run better.  Sweet!