The Ford Barn

exoilfld · 10-22-2025, 12:29 PM

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?

mfirth · 10-22-2025, 03:07 PM

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

Doublepumper · 10-22-2025, 06:24 PM

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

hueyhoolihan · 10-22-2025, 06:28 PM

Quote:

Originally Posted by Doublepumper

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

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

Flathead Fever · 10-22-2025, 10:24 PM

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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.

10-22-2025, 12:29 PM	#1
exoilfld Senior Member Join Date: May 2010 Location: alto, tx Posts: 155	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?

10-22-2025, 03:07 PM	#2
mfirth Senior Member Join Date: Aug 2017 Location: ohio Posts: 1,165	Re: Backfire I'd check for a vacuum leak, maybe lean fuel .... ??? Backfiring through the carb sure can damage the power valve.

10-22-2025, 06:24 PM	#3
Doublepumper Senior Member Join Date: Aug 2017 Location: WA-OR, USA Posts: 102	Re: Backfire Incorrect firing order or valve lash too tight are a couple other causes. __________________ Ever stop to think and forget to start again?

10-22-2025, 10:24 PM	#5
Flathead Fever Senior Member Join Date: May 2010 Location: Yucaipa, CA Posts: 1,492	Re: Backfire Sponsored Links (Register now to hide all advertisements) 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. Last edited by Flathead Fever; 10-22-2025 at 10:36 PM.