The Ford Barn

Tribalmonkey · 08-24-2021, 01:52 PM

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?

chrs1961815 · 08-24-2021, 02:23 PM

Does it backfire through the carb or the muffler?

Tribalmonkey · 08-24-2021, 03:41 PM

Quote:

Originally Posted by chrs1961815

Does it backfire through the carb or the muffler?

Through the muffler.

Big hammer · 08-24-2021, 03:47 PM

GAV adjusted to lean, intake leaking, carburetor float set to low

ETAModel · 08-24-2021, 03:51 PM

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.

Tribalmonkey · 08-24-2021, 04:23 PM

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Quote:

Originally Posted by ETAModel

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.

Doesn’t that sound opposite? Doesn’t that make it even more rich?

Tribalmonkey · 08-24-2021, 04:31 PM

Also, I don’t understand why that would be different now when all I have done was replace plugs and wiring.

noboD · 08-24-2021, 04:34 PM

How old is the gas?

Tribalmonkey · 08-24-2021, 04:41 PM

Quote:

Originally Posted by noboD

How old is the gas?

About a week old.

Tribalmonkey · 08-24-2021, 04:50 PM

Quote:

Originally Posted by ETAModel

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.

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.

jg61hawk · 08-24-2021, 05:06 PM

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/showt...hlight=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.

Tribalmonkey · 08-24-2021, 05:13 PM

Quote:

Originally Posted by jg61hawk

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/showt...hlight=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....

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.

Jacksonlll · 08-24-2021, 05:37 PM

Make sure you don’t have an intake leak at manifold and carb flange. Make sure. Sometimes hard to find.

Synchro909 · 08-24-2021, 07:14 PM

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.

Tribalmonkey · 08-24-2021, 07:48 PM

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.

nkaminar · 08-24-2021, 08:33 PM

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.

nkaminar · 08-24-2021, 08:42 PM

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.

johnbuckley · 08-25-2021, 02:47 AM

sorry wrong post.

Ernie Vitucci · 08-25-2021, 12:51 PM

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

08-24-2021, 01:52 PM	#1
Tribalmonkey Junior Member Join Date: Jan 2021 Posts: 25	Roadster Backfiring 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?

08-24-2021, 02:23 PM	#2
chrs1961815 Senior Member Join Date: Jul 2018 Location: Spring Grove, Illinois Posts: 1,371	Re: Roadster Backfiring Does it backfire through the carb or the muffler? __________________ "The more things change, the more they stay the same."

08-24-2021, 03:51 PM	#5
ETAModel Senior Member Join Date: May 2013 Location: Along the Red River, Texas Posts: 360	Re: Roadster Backfiring 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.

08-24-2021, 04:31 PM	#7
Tribalmonkey Junior Member Join Date: Jan 2021 Posts: 25	Re: Roadster Backfiring Also, I don’t understand why that would be different now when all I have done was replace plugs and wiring.

08-24-2021, 04:34 PM	#8
noboD Senior Member Join Date: May 2010 Posts: 319	Re: Roadster Backfiring How old is the gas?

08-24-2021, 03:47 PM	#4
Big hammer Senior Member Join Date: Jun 2014 Location: Land of Lincoln Posts: 3,127	Re: Roadster Backfiring GAV adjusted to lean, intake leaking, carburetor float set to low __________________ Don't force it with a little hammer tap, tap, tap get a bigger hammer tap done

08-24-2021, 05:06 PM	#11
jg61hawk Senior Member Join Date: Oct 2014 Location: Central New Jersey Posts: 404	Re: Roadster Backfiring 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/showt...hlight=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. Last edited by jg61hawk; 08-24-2021 at 05:12 PM.

08-24-2021, 05:37 PM	#13
Jacksonlll Senior Member Join Date: Jul 2012 Location: Michigan-- Member of Oakleaf of MARC Posts: 1,686	Re: Roadster Backfiring Make sure you don’t have an intake leak at manifold and carb flange. Make sure. Sometimes hard to find.

08-24-2021, 07:14 PM	#14
Synchro909 Senior Member Join Date: Jun 2014 Location: Melbourne, Australia Posts: 7,496	Re: Roadster Backfiring 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. __________________ I'm part of the only ever generation with an analogue childhood and a digital adulthood.

08-24-2021, 07:48 PM	#15
Tribalmonkey Junior Member Join Date: Jan 2021 Posts: 25	Re: Roadster Backfiring 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.

08-24-2021, 08:33 PM	#16
nkaminar Senior Member Join Date: Jan 2012 Location: Western North Carolina Posts: 3,899	Re: Roadster Backfiring 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. __________________ A is for apple, green as the sky. Step on the gas, for tomorrow I die. Forget the brakes, they really don't work. The clutch always sticks, and starts with a jerk. My car grows red hair, and flies through the air. Driving's a blast, a blast from the past. Last edited by nkaminar; 08-24-2021 at 08:45 PM.

08-24-2021, 08:42 PM	#17
nkaminar Senior Member Join Date: Jan 2012 Location: Western North Carolina Posts: 3,899	Re: Roadster Backfiring 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. __________________ A is for apple, green as the sky. Step on the gas, for tomorrow I die. Forget the brakes, they really don't work. The clutch always sticks, and starts with a jerk. My car grows red hair, and flies through the air. Driving's a blast, a blast from the past.

08-25-2021, 02:47 AM	#18
johnbuckley Senior Member Join Date: Jul 2010 Location: United Kingdom Posts: 1,441	Re: Roadster Backfiring sorry wrong post. Last edited by johnbuckley; 08-25-2021 at 02:57 AM.

08-25-2021, 12:51 PM	#19
Ernie Vitucci Senior Member Join Date: May 2016 Location: Scottsdale, Arizona Posts: 611	Re: Roadster Backfiring 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