I have a 1979 F150 4x4 351m 2 barrel carb, the question i have is: what would cause my truck to backfire thru the exhaust when i let off the gas, it was great when im doin 65-70 mph as i let off the gas it backfires, i see flame coming out, any ideas ?
Little too rich a mixture from the carb during closed throttle, you may not be able to rectify the problem even with a carb overhaul with this stuff they call fuel today, but you might try using some StaBil Marine addiative to the fuel tank, this helps nullify some of the effects of today's fuels on older systems. HTH
Just the opposite described not too rice, It is too lean ! Use gumout carburator cleaner with red tube nozzle , fill the bowl by shooting spay in through the vent. several attempts may loosen low speed jet clogged particulate as well as main jet particulate I have found this too rectify back firering when decelerating or downshift/deceleration
An exhaust leak can cause backfires. Air sucked into the exhaust can burn excess gasoline.
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