I'm not positive - but I don't think he meant the idle screws were not
working. What he was saying is that adjusting the idle screws has no
effect on the lean response under very light acceleration. He did say at
one one point: "I can turn in the idle mixture screws a 1/2 turn or more
until it makes a difference and the revs drop off hard"
So it looks like the idle circuit is working it just doesn't have any
effect on the problem of the mixture going lean under light load, which
The carb's a 650cfm double-pumper ser# 4777 which the PAW catalog lists as
a "STREET/STRIP Series Carb". I wouldn't call it a race carb exactly but
understand that some Holleys use more jet and less PV flow (through smaller
Power Valve Channel Restrictors PVCR) which can account for less mileage and
more performance. I replaced the primary jets just in case someone drilled
the originals. Everything is stamped with original specs for the carb.
The idle mixture issue was included in case it sounds related to someone
but should have no noticeable effect at cruise since you're already beyond
the transition slots and relying on jets with the PV for enrichment. All
idle adjustment was referenced at idle only. The idle screws appear fine.
If there was some gum in the carb, it should've loosened up over the past
5,000 miles with a clean tank, running clean fuel through a new filter with
carb/injector cleaner additive on top of all this, right? I can throw in
the towel and tear the carb to pieces but I'd like to explore tuning first.
Is there a way to check if some passages are clogged (blow through idle
screw holes, etc.) without removing the carb completely?
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