CB1100 Idle speed instability problem

[peterbaron]

Enzo there are 4 calibrated gauges required together with the knowledge to deal with the interaction of the iacv positions.

From the question i think you may not have done a carb/ throttle body sync before, so before changing anything i would suggest to watch several yt video's to find out what's involved, how to do it and why.
Throttle sync is only required when the engine is warm and at idle, there is no other reason to adjust the sync adjustment which is why Honda does not supply service info, they want to avoid the risk of getting it wrong which is easy to do, the adjustment screws are not fixed like the old carburettors so by adjusting too much you can drift out of range and end up with a rich or lean mixture.
With carburetors you adjust the amount of fuel mixture, with a throttle body you only adjust the amount of air per cylinder, there is a difference.

For instance when i bought my cb919 the engine sounded like a harley at idle, the engine only ran on 2 cylinders, it took me a while to work out why, and after syncing the throttlebody with the 4 gauges it started to run like it should have; somebody mis-understood what they did and got it wrong.
Once i had the vacuum gauges installed and started the engine it was very apparent that the sync was off.
All four cylinders have the same capacity so they produce the same amount of vacuum at each intake stroke at the intake when the valves open, this amount can be measured with 4 individual vacuum gauges and adjusted so they read the SAME amount of vacuum supplied through the iacv and adjusted ( equalized ) by the 4 screws under the throttle body.

As soon as the throttle is opened slightly the butterfly valves and the tps start doing their job and the idle screws are no longer of any importance, they are only required when the butterfly valves are closed.

You can then verify this by using a piezo electric pressure sensor in the exhaust and watch the pulses it produces with each exhaust stroke which should be equally the SAME, you do need an automotive oscilloscope for this check so you can record and watch the pulse train.
Hope this helps.

My advice; if there is no problem don't introduce one.
With all respect for your ability and thanks for all your help, i appreciate it; cheers

**

"My advice; if there is no problem don't introduce one."


Sage advice quite often.

Agree with both...if NFF = do not tinker