2000 454 mag , Holley carb backfires
 

I have a 87 Baja 240 sport. It has an 2000 454 mag. with a Holley carb. A couple of years ago i wrote in on how my plugs are not burning right. It was good at higher rpm, but do alot of idling through channels. I was burning premium gas at the time and took the advice from this forum to run a lower octane gas. that worked fine except when i shut the motor off it spits or backfires one time before it done. I was wondering if its a carb issue or timing issue. thanks for your time. Dan

it could be either or both.can you give some info on your setup,i don,t remember your thread.i will say that run on after the key is shut off is often caused from the idle speed being to high.

Thanks, Its a stock 2000 454 mag. with a 750 Holley vacuum secondaries . It only spits once, it never did that when i using premium gas.

Your idle may be a little to high causing boosters to be flowing fuel or your float level is way to high causing fuel to dribble in the throttle bores.

This will cause run on....ie: one to many combustion events with the ignition off.

edit in: higher octane fuel may supress this, however, in this case, higher octane is not the fix. Idle rpm or carb tuning is.

Thanks, I will tune the carb and see what happens. This Holley has not been tuned or rebuilt in a few years. Boat sits alot in storage for the winter, so I"m just getting it ready for this year. I have an electronic fuel pump, so as far i know there is no need to start motor to adjust floats, correct?