I have a 305 with a carter afb 4 barrel carb on it.

It will only backfire when its sitting at idle and i try to punch it slightly. It happens about once out of ten times. It actually caused my carb to catch fire and I had to get a policeman put it out with an extinguisher. I took apart the carb and cleaned the whole thing top to bottom, the gaskets still looked good (rebuilt it about 4 months ago), put it all back together and its still backfiring.

The carb is a little to big for the engine, I believe? its a 650cfm carb.

So, what I have read is that my timing is off or I am running too lean. Would that make sense for my situation?

Sorry, I'm a little new at carburetors.

Thanks

Yes.

Check the timing first and yes, could possibly be a lean pop. Haven't had one fart fire at me for a long time but it was usually a timing issue. Also, I hope you're not using one of those foam triangle air cleaners...

Yes, originally it was the edelbrock one . I took out the foam because It has a gaping hole in it from backfiring already. I have mesh inside the air-ram so I figured it would be safe till I came up with an alternative.

Well I figured out some of the problem.. One of the studs holding down the carb and spacer were completely stripped out. So I got new gaskets and all new studs and nuts and it hasn't backfired on me since. Just need someone to tune the carb.

Thanks for the help

Check all your plug wires, make sure there's no shorts or breaks in them. Make sure they are all securely on the plugs and dist. Recheck firing order. In my experience, backfires are usually an ignition issue, not a fuel issue.

i just yesterday cleaned the rotor button and cap on my sisters 83 monte carlo 305...i had to take off the plug wires...and when i put it back on i had 2 wires swapped around....it idled fine and ran but when i punched it at idle it would backfire...you might make sure that your plug wires are right.

I checked the firing order and it looks good. And they are all secured to spark plugs and distributor. Tonight I'll run a continuity test on all the wires to check for breaks in the wires, there is no visual cracks or breaks.

Would old spark plugs cause backfiring? They look like they could use a replacement..

Also, it has a 650cfm carb on it. What I've read is that for a 305, you should really have a 500cfm or 550 at the most.. would this also cause backfiring because the vacuum created by the carb isn't working correctly for the motor?

Thanks

650 will be fine, I ran a 750 on my 305 without a problem for a few months before dropping in my current 350. What's you're timing at?