Team, have a question/idea for discussion. We are all (mostly) aware of the situation with the throttle body linking screws; not to be touched etc. However sometimes a PO seem to have gotten to them anyway (always a Previous Owner of course ).

From the factory the original setting is done with a flow bench, which is understood to be more precise than with vacuum equipment on the bike. I once tried to make a box where I could fit the TB's on with some old stubbs to see if I could get them better adjusted off the bike with a shop vac at the end. This didn't work (for me) as somehow the air flow wasn't even through the bodies. After too much local recipe (I'll leave that to your imagination) I thought what if we were to use an anemo meter to measure the air flow through the TB's individually to adjust/check them? Something like THIS

We wouldn't be interested in absolute, genuine measurements, so calibration etc is not required. Repeatability however is, as you need to measure each TB individually. I'm certain one could quickly come up with an adaptor between the tool and the TB. With an old (or current) vacuum cleaner at the other end you should then be able to do a proper adjustment or check.

Any ideas/comments/faults/remarks/critisism on the above??

a good thought rene

one would need to be assured that the flow available through each tb would be equal to start with ... a balencing or difference mesurement would be all that might be required ...the anemometer would give a more or less measurement of the amount of flow at a relative setting ...and verry hard to duplicate the particular throttle setting accross all the tbs on multiple runs ,
maybe a precission cut length of tube with a take off port also precission made, applied to the out side of the tbs x 4 could give a vacume measurement ,,,(outside the internal jetting bypass arangements) for relative measurement with butterfly openings a push type air pump would be good in this case ? at the inlet side ..probably carb sticks could do the job ? as we're interested in flow right through the range of throttle openings ?

just a thought to add to the mix

Charlie, thought about that one as well, but following my earlier attempt I think it might have to be individual per TB or 4 long hoses to a collector to even out pressure differences. To be clear I'm thinking of adjustment with the rack off the bike. The vacuum cleaner would give you a constant 'vacuum' to measure with. To visualise; a vacuum hose connected to the throttle body bottom and the anemometer on the top. Adjustment on the bike would be with the 'by-pass screws' only.

If you plan on taking the TB's off, why not try the reverse of vacumn(blowing) through onto the manometer, only say this as it is soo difficult to form a vacumn, my thinking is you would still achieve the same result albeit positive pressure rather than negative, most of us have access to a compressor with a regulator.
Just a thought

If you feel the T/B's have been tampered with then using a cone shaped spacer to plug the meter into and connect to the Top of the T/b will allow you to check each one inturn as long as you can get a good clean fit for the vacumn cleaner most would think the vacumn cleaner would run constantly for long enough to check them all after all they go for a fair time in the house each time we use it. i cant think of a reason why it would not work. Especially if you have a good set ready to trust as a guide. by the same token a vac gauge from a car should do the same job??????? must be dozens laying about in wrecker yards by now? And the whole thing is to finesse the units isnt it?

You are making this too hard. I adjust the throttle plates on my Ks, and this technique was passed to me by a fellow who worked in Research at BMW building and testing the original K-100 and K-75 prototypes.

With the engine fully warmed, loosen the TPS and disconnect the electrical connector if it is an L-Jetronic bike. Turn the bypass screws on all of the throttle bodies in until seated. Turn the idle screw out to increase the idle. This compensates for having closed all the bypass screws. Attach your mecury manometers. Somewhere on the hose to the rearmost TB you should have a T-fitting to which you attach the vacuum hose from the fuel pressure regulator (normally this hose attaches to the spigot on the rear most TB). Now start the engine and set the idle around 1000 or so. Pinch the hose from the rearmost TB to the fuel pressure regulator shut after the engine has run a few seconds.

Now, turn the screw between TBs 1&2 such that the mercury colums are equalized. Next turn the screw between the rearmost pair of TBs to equalize the heights of their respective mercury columns. At this point the front pair of mercury colums will be the same height and the rear pair will be paired at a different height. Now, turn the screw between the second and third TB. As you move this screw you will see the two pairs of mercury columns move, each pair moving together as a pair. Set both pairs at the same height and you have successfully set the throttle plates to the same position when fully closed. See, that wasn't so hard.

The next step is to turn each bypass screw out one turn. Turn the bike on again and use the screw on the throttle shaft to set the idle speed at 1000. After this, never again adjust your throttle speed using that screw. Why? Moving that screw moves the whole throttle shaft and that moves the shaft relative to the TPS and it screws up your TPS setting. In the future, you will always without exception set idle speed and balance together using the bypass screws. You are almost done.

Since the bike is hot and you still have the manometers connected, you can touch up TB balance. Pinch the hose to the fuel pressure regulator shut again, and adjust the bypass screws if any minor adjustment is required. When that is complete, remove the hoses for the manometers, put the rubber plugs over the spigots and put the hose from the fuel pressure regulator on the rear most TB spigot. When all of this is done, set the TPS to the correct position (feint click heard just as the throttle is opened), put the connector back on and you are done.

Happy riding.

+1 very nice explanation

I think thats about what I worked out when I did it, though of course I went at it ass backwards. The early motronics bikes don't have the vacuum fpr but they do have an electronic mixture adjustment called 'idle adjustment'

The only thing I would add is that just about anything can (apparently) screw up the tb balance; a cruddy spark plug, a loose tappet, clogged injector, tracking ht etc. You wind up compensating for other faults. So this should be the last thing done in a service routine.

[quote="GerryP"]+1 very nice explanation

I think thats about what I worked out when I did it, though of course I went at it ass backwards. The early motronics bikes don't have the vacuum fpr but they do have an electronic mixture adjustment called 'idle adjustment'

The only thing I would add is that just about anything can (apparently) screw up the tb balance; a cruddy spark plug, a loose tappet, clogged injector, tracking ht etc. You wind up compensating for other faults. So this should be the last thing done in a service routine.[/quote]

Correct. You want to be certain all valve clearances are within spec, fresh spark plugs and there are no vacuum leaks before adjusting throttle plates. I neglected to state that at the outset of my explanation.