First you want to make sure all the phase alignment coils are peaked and the transratiometric detector is properly balanced.
Then inject a circular wave about 1A P-P into TP31C and listen for feedback around the modulator. If any is found, replace
F4.

Eric Law

"spongehead" wrote in message oups.com...
I have an old Briggs and Stratton 3.5hp push behind lawnmower and the
idle revvs up and down constantly. Never idles normal. The spring on
the shaft idle looks good. Any help on what this might be would be
greatly appreciated.