Quote:
Originally Posted by priobe
Idle your motor up to where you are experiencing the problem with idle screw. Then shut off the motor. Look at the relation of the throttle plate to the progression holes ( if I got this right) if the progression holes are under the throttle plate then additional holes could possibly help.
If the progression holes are above the throttle plate then the additional would not help.
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To make it easier still, you could leave the engine running at the high idle speed and simply turn the idle screw in a little and see if the engine gains rpm.
If the engine gains rpm, then you are too rich at that point (idle jet / air corrector combination).
If the engine looses rpm, it may be the correct idle jet / air correct combination, but proceed by now turning the mixture screw out a little.
If the engine gains rpm it needs a richer idle jet / air corrector combination.
If the engine looses rpm
and the loss is comparable to the loss of rpm when you turned the mixture screw in (a comparable amount) then the idle jet / air corrector combination is likely ideal.
Basically, you can turn the idle speed up to where ever you like (within the idle / off-idle circuits range of operation) and do a rich / lean test with an idle mixture screw. Again, if leaning the mixture screw causes the engine to gain rpm, it's too rich at that point. If leaning the mixture screw causes the loose rpm it either has the correct a / f ratio or is lean - follow up by richening the mixture screw to confirm the prior diagnosis.
NOTE: you may need to lean or richen more than one mixture screw.
You must tune from the bottom up, meaning start with the idle & off-idle (transition), then work into the main circuit. The main jet size as well as the main air corrector and emulsion tube all play a part in the activation point of the main circuit - and
together with the idle jet / air corrector combinaton determines the overlap between the two circuits.
Troy Patterson