Roadster Backfiring

T

Tribalmonkey

Junior Member
I know this has been discussed a bunch of times. I’ve read through many of the related threads but have not found a solution.

I rewired my roadster including the ignition. I also installed new plugs (gapped). Now it backfires really bad when I let off the throttle and going downhill under load. It didn't do this before. What can I do to fix this? What should I check?
 
I am new to the A, and got lots of advice on where to set the Gav. Also was trying to improve my mpg. When I closed the Gav too much she would backfire every time I got off the foot feed.
Sounds like you have the same problem. Try opening the Gav. And see what happens.
 
ETAModel said:
I am new to the A, and got lots of advice on where to set the Gav. Also was trying to improve my mpg. When I closed the Gav too much she would backfire every time I got off the foot feed.
Sounds like you have the same problem. Try opening the Gav. And see what happens.
Click to expand...

Doesn’t that sound opposite? Doesn’t that make it even more rich?
 
ETAModel said:
I am new to the A, and got lots of advice on where to set the Gav. Also was trying to improve my mpg. When I closed the Gav too much she would backfire every time I got off the foot feed.
Sounds like you have the same problem. Try opening the Gav. And see what happens.
Click to expand...

The only logic I can see with this is that running too lean makes your engine run hotter. Maybe that create more opportunities for combustion in your muffler.
 
You go to this thread post #4 and you start there... Get a carb rebuild by BUllock and then you have solved 99% fuel problems...
https://www.fordbarn.com/forum/showthread.php?t=293126&highlight=bullock
I have a rebuilt Bullock carb, GAV (oh the mystery GAV) is turned out about 1/2 and NEVER touched. My car did all sorts of crap before I got a real carb rebuilt by this guy... GAV, and all the rest are BS after the carb is restored to new.... they were made to run....I can't say enough about the difference in starting and running since my carb by Bullock.
 
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jg61hawk said:
You go to this thread post #4 and you start there... Get a carb rebuild by BUllock and then you have solved 99% fuel problems...
https://www.fordbarn.com/forum/showthread.php?t=293126&highlight=bullock
I have a rebuilt Bullock carb, GAV (oh the mystery GAV) is turned out about 1/2 and NEVER touched. My car did all sorts of crap before I got a real carb rebuilt by this guy... GAV, and all the rest are BS after the carb is restored to new.... they were made to run....
Click to expand...

Not saying that a carb rebuild wouldn’t help… but it ran fine Sunday. I didn’t touch the carb and now it is backfiring really bad. I messed with the electrical. All associated ignition wiring and new plugs. I have gone back through the wiring but I didn’t see anything.
 
All the symptoms of a leak in the intake tract somewhere. Something that hasn't been mentioned is the rotor button. They are known to track to earth and you can't see where. Try a known good one. Also check you are not getting the infamous Model A no 3/4 cross fire.
 
So I just drove it with the GAV open almost an extra full turn and it didn't backfire. I'm trying to make logic from that. Why would running richer be better? Why would running leaner cause backfire.
 
Nothing you did to the electrical caused the problem. The two are unrelated. You need to clean out the carburetor.

Lean will cause the backfiring. A jet or passage that is partially blocked in the carburetor will cause it to be lean. Opening the GAV will compensate for the blocked jet or passage.
 
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i think the backfiring when lean is because the combustion is not complete. Any combustion that does take place is hotter. So fuel and oxygen are pumped out into the exhaust system and ignite.
 
Good Morning...You might also have a condenser that is starting to go bad. They do this when they are about done...Get a good one (more expensive) the really cheep ones are not any good...Ernie in Arizona
 
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