OK, I have an 85 K100RT.
I understand that to do a good tune up I should check the valve gap then check/adjust the timing.

Now when it comes to the fuel adjustments I'm a little confused.

I have a set of good mercury carbstix. I understand that unlike the flat twin airheads, you do not adjust for maximum when adjusting the fuel/air screws. But what is the correct way? Last time I did it. they were all a little off so I just tweaked them till they were all kinda level with each other.

But how can I tell if they are all equal in the RIGHT PLACE?

Then once I get that fuel/air mixtrure right, how do you balance the four
cylinders using the adjustment screws on the throttle bar?


Gee, I wish this was a simple as the old R bikes.

When they all is in level at idle , you're good.....if the idle is to low/high, adjust the screws equally a very tiny amount out/in.

You could also adjust the idle rpm at the adusting screw for all the TB's, but then you also have to adjust the TPS.

You don't adjust the fuel/air mix (the Jetronic unit takes care of that) but the amount of the mixture, if needed the fuel/air mix at idle can be adjusted at the AFM unit.

Puccini wrote:Then once I get that fuel/air mixtrure right, how do you balance the four
cylinders using the adjustment screws on the throttle bar?

If you're referring to the inter-linkage screws (the silver ones each with a locking nut), don't touch them at all.  They are set at the factory and are meant never to be readjusted.  Only touch the brass coloured air bypass screws and maybe possibly the throttle main adjust screw (which is really a throttle stop screw).

Inge K. wrote:When they all is in level at idle , you're good.....if the idle is to low/high, adjust the screws equally a very tiny amount out/in.

You could also adjust the idle rpm at the adusting screw for all the TB's, but then you also have to adjust the TPS.

You don't adjust the fuel/air mix (the Jetronic unit takes care of that) but the amount of the mixture, if needed the fuel/air mix at idle can be adjusted at the AFM unit.

Right but heres the problem.

I attach the mercury stix. The four tubes will not be at the same height.

So I can adjust the screw for air/fuel mixture at idle so they are even.

Is that all you  do?

Is there some way, with carb stix, to know when the air/fuel mixture at Idle is at the best position for each cylinder. I mean do you adjust the air/fuel mixture screw till the mercury goes to the highest point you can get in the mercury column?

Very confusing

Inge K. wrote:When they all is in level at idle , you're good.....if the idle is to low/high, adjust the screws equally a very tiny amount out/in.

You could also adjust the idle rpm at the adusting screw for all the TB's, but then you also have to adjust the TPS.

You don't adjust the fuel/air mix (the Jetronic unit takes care of that) but the amount of the mixture, if needed the fuel/air mix at idle can be adjusted at the AFM unit.

Whats a TPS?? Remember this is my first experience with the K100 tune up.

Puccini wrote:I attach the mercury stix. The four tubes will not be at the same height.

That isn't normally a problem......you maybe have got a intake leak.

Puccini wrote:Whats a TPS?? Remember this is my first experience with the K100 tune up.

TPS = throttle position switch......you find it at the rear end of the TB's,
it only senses fully closed and fully open throttle.

This site has several threads which already discuss this procedure.  Here are some URLs:
https://www.k100-forum.com/t1526-how-to-balance-the-throttle-bodies-solved
https://www.k100-forum.com/t3880-what-is-the-correct-procedure-for-synching-throttle-bodies-on-91-k100rs-4v
https://www.k100-forum.com/t5671-16valve-throttle-body-sync

You'll want to adjust for RELATIVE balance, not ABSOLUTE vacuum.  This means, the columns on the Carbstix should be at the same level relative to cylinder 1; what the level is in absolute mmHg does not factor into the balancing process.  As Inge pointed out, AFR is set by the Jetronic computer.  This is an old analog EFI system with open loop characteristics.  Some adjustment of the AFR can be achieved by carefully tweaking the CO mixture adjustment on the mass airflow sensor within the air box.

The brass coloured air bypass screws have two purposes in life (1) fine adjustment of the air drawn by each cylinder through its respective TB until all are drawing the same volume of air at idle (2) setting the idle speed of the engine once (1) is achieved.  Please note, (1) cannot be achieved until all other elements of the engine are working as designed.  That is to say, no air leaks into the intake system, no split or deteriorated hoses, no leaking rings, no maladjusted valve gaps, etc.  If any air bypass screw needs extraordinary adjustment relative to the others, that's a pretty good indication that something is amiss.

TPS means Throttle Position Sensor.  This is the switch on the end of the throttle body assembly that detects fully closed and fully open throttle butterfly position.  This device needs to be set once balance is achieved in the sync process.