Backfire
 

I have a new French flathead with an 8ba front and 59ab bell housing converted to 12 bolts with a new vacuum distributor and new carb. It runs good at idle but backfires through carb on accleleration. Timing with vacuum attached is about 2 degrees. I have replaced the power valve but no change. Any ideas?

Re: Backfire
 

I'd check for a vacuum leak, maybe lean fuel .... ??? Backfiring through the carb sure can damage the power valve.

Re: Backfire
 

Incorrect firing order or valve lash too tight are a couple other causes.

Re: Backfire
 

lordy...i'd sure be hoping i'd screwed up the firing order. ha

Re: Backfire
 

Like others have said I'd check the firing order. Remember that the cylinder numbering on a flathead is not the same as other Ford V8's. You can have two cylinders mixed and it might idle just fine until you step on the gas. There is lots of diagrams on YouTube to double check it. If that doesn't fix it, then you need to figure out if it's fuel or engine mechanical. You can try spraying a can carb cleaner into at the spot it misses at and see if it gets better. That might determine if it's a fuel problem or something else.