Backfire issue

[413Polara]

Hey guys. I’ve recently, within the last two weeks, put an edelbrock rpm performer intake on my 413. It ran great to a couple shows last week and all of a sudden in the last couple days it’s started backfiring. You can hear it popping out the exhaust and a couple times sounded like it came back through the carb under the hood. When it’s not fully up to temp it seems to be a guarantee it will happen, once it’s warmed up its hit or miss. Just had it out and it ran great, earlier today it was doing it then all of a sudden it stopped and it ran great. Carb is a 750 summit. I haven’t found any noticeable vacuum leaks, everythings tight under the hood. Maybe a timing issue? Car has a pertronix ignition that previous owner installed. Any suggestions would be appreciated.

 

[RemCharger]

Could be a burnt plug wire. Check them all carefully

 

[Project66]

Backfiring often happens when your mixture is too lean. I had that kind of issue a few years ago and I found that the plug on my carburetor's power brake port had come off. That makes me suspect that you might have a leak somewhere in your intake manifold gasket.

 

[ruffcut]

I was thinking a plug wire also

 

[LowBikeMike]

Backfiring thru the exhaust is the result of unburnt fuel in the exhaust mixing with some oxygen. Thru the carb is generally a lean condition. You need to figure out which end it's coming from.

 

[68-500]

New intake, same carb as before? Id also look at intake gasket leaks.

 

[413Polara]

Does it make sense for it to run fine for a week then start acting up if it’s an intake gasket? I should have also added that it only seems to backfire under load. I’m neutral you can rev it all you want and it never backfires. The car has always kind of fell on its face at wide open throttle since I bought it which is another issue I’m trying to sort out. Maybe there’s a connection?

 

[68-500]

A few heat and cool cycles who knows. Id put a wrench to the bolts for sure

 

[Geoff 2]

If it runs great some of the time, you can rule out wiped cam.
My first thought starts with P.....Pertronix.
It could also be poor connections. Find the wiring diagram for that particular Pert module. Run a jumper from the +ve connection of the Pert direct to the bat +ve terminal & test drive. This will bypass the ign sw, bulkhead connectors etc. These areas are where you would need to look if the jumper fixes the problem. You will have to remove the jumper to stop the engine.