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Old 07-26-2020, 07:23 AM   #2
30 Closed Cab PU
Senior Member
Join Date: Aug 2018
Location: Wisconsin
Posts: 2,290
Default Re: Backfire in overrun mode (load change)

Carb maybe running lean, try giving the GAV another 1/4 turn CCW, then another 1/4 turn CCW. I find that my Gav has to be set at 1/2 turn open, otherwise I get a little popping/cough when decelerating and when upshifting gears.

Possible intake manifold leak. With fan belt off and motor running spay wd40 around the intake manifold and listen for a change in motor running. Not sure from your description above, when changing manifolds supposed to have then surfaced as a pair, also the copper manifold gaskets are recommended. Also try WD40 with motor running around the Carb/Intake manifold seal and listen for motor running change.

Some use a propane torch (unlit) instead of WD40.
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