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Carburetor backfire with rebuilt carbs
Posted by: Kamaka ()
Date: August 11, 2019 05:39PM

The car is a 66 Corsa 140 with AC. The car has 65 linkage on it.

I recently replaced all 4 carbs with Clarks Rebuilt ones.

The original carburetors ran ok but surged on the highway, so I figure since it has been 15 years since I rebuilt them, I would buy the rebuilds from Clarks and all would be good. I purchased 65 carbs to match the linkage.

I sync'd the carbs, set the chokes, idle mixture, etc. The car runs good BUT occasionally backfires through the primary carburetor on the right bank. I just got it running today but I found it odd that it was doing it. I'm going to check the timing next and maybe even pull the valve cover to be sure everything looks good.

I know that typically popping through the carb is because ignition is occurring in the intake manifold and usually it means a valve problem. BUT since the only thing I changed was the carbs and it ran fine before I do not think this is the case.

Any Thoughts?

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Re: Carburetor backfire with rebuilt carbs
Posted by: alphasud ()
Date: August 11, 2019 05:51PM

Right side carb too lean causing a misfire? What happens when you richen up the idle? Check ignition wires to make sure you didn’t get them routed wrong. I know the ford 302 has to have wires isolated from each other. Too close and they will cross fire. Maybe your wires are tired or cap for that matter. Only other would be a intake valve hanging.

David North Idaho
1965 Corsa Turbo converted to 140
1971 Super Beetle with 2.5L Subaru engine
2004 F350 work truck
2004 Cayenne Turbo

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Re: Carburetor backfire with rebuilt carbs
Posted by: Kamaka ()
Date: August 11, 2019 06:13PM

Good point. I will check the wires- they are old but do not have many miles on them BUT i did reroute them! AND I tie wrapped them too! I can't wait to get check!

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Re: Carburetor backfire with rebuilt carbs
Posted by: 2ragtops ()
Date: August 11, 2019 06:51PM

I just bought two from Clarks and one of them was backfiring

Bob Bauer

Show-Me Corvairs

1966 Monza Convert 140 P/G with A/C, plastic wheel with tele-column am-fm posi-traction
1966 Corsa Convert 180 wood wheel tele-column am-fm sport steering posi-traction
1965 Corsa Coupe Crown V8 temporarily red lined for repair
House Springs, Missouri

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Re: Carburetor backfire with rebuilt carbs
Posted by: Kamaka ()
Date: August 11, 2019 06:56PM

How did you fix it?

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Re: Carburetor backfire with rebuilt carbs
Posted by: 2ragtops ()
Date: August 11, 2019 08:01PM

I haven't yet. Not sure it is the carb. Checking valves tomorrow

Bob Bauer

Show-Me Corvairs

1966 Monza Convert 140 P/G with A/C, plastic wheel with tele-column am-fm posi-traction
1966 Corsa Convert 180 wood wheel tele-column am-fm sport steering posi-traction
1965 Corsa Coupe Crown V8 temporarily red lined for repair
House Springs, Missouri

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Re: Carburetor backfire with rebuilt carbs
Posted by: RexJohnson ()
Date: August 11, 2019 08:55PM

If it didn't back-fire thru the carb before you switched the carbs then I would be looking at what you just did. As the wires being moved could cause the problem or the problem could be the carb itself. I would try swapping the carbs side to side and see if the problem moves to the other side. If it does then it is the carb. I would not be pulling a valve cover at this time.

RJ tools
Salem,Oregon

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Re: Carburetor backfire with rebuilt carbs
Posted by: Frank DuVal ()
Date: August 11, 2019 09:20PM

Make sure the carburetor is sealing to the intake manifold (head). If there is a vacuum leak there it can cause a lean backfire through the carburetor.

Are you running the insulator there?

Frank DuVal

Fredericksburg, VA

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Re: Carburetor backfire with rebuilt carbs
Posted by: Kamaka ()
Date: August 12, 2019 03:48AM

Yes, insulators with gaskets. I'm going to check the timing too It is possible that while wrestling the AC compressor that i bumped the distributor

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Re: Carburetor backfire with rebuilt carbs
Posted by: vairmech ()
Date: August 12, 2019 04:48AM

If you are running points I would check the gap, If you are running a Pertronics put points in and see if the issue goes away.

I just went through the same backfiring issue, I pulled the tops off the carbs looking for issues and other than a little dirt in the bowls - nothing. I reset the points and all is well.

Ken Hand
Handy Car Care
248 613 8586

Vairmech@aol.com

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Re: Carburetor backfire with rebuilt carbs
Posted by: corventure Dave ()
Date: August 12, 2019 08:07AM

I have also found that having too rich or large sized main jets in the Secondaries can cause carburetor backfiring. I solved this on several 140's by rejetting.

Corventure Dave



Edited 1 time(s). Last edit at 08/12/2019 08:09AM by corventure Dave.

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Re: Carburetor backfire with rebuilt carbs
Posted by: 66vairman ()
Date: August 12, 2019 08:33AM

Two things:

1) Does the carb backfire while idling, cruising, or when the accelerator is depressed?

2) If the car still surges on the highway with the new carbs the timing may be too advanced. Sometimes the vacuum advance spring gets weak and pulls in full advance too early. Weak, broken, or incorrect mechanical advance springs can cause to much timing advance at a given RPM.

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Re: Carburetor backfire with rebuilt carbs
Posted by: Timothy Shortle ()
Date: August 12, 2019 12:51PM

Too lean fuel mixture and/or too late ignition timing setting.

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Re: Carburetor backfire with rebuilt carbs
Posted by: 2ragtops ()
Date: August 12, 2019 03:55PM

reset the dwell and timing, backfire went away

Bob Bauer

Show-Me Corvairs

1966 Monza Convert 140 P/G with A/C, plastic wheel with tele-column am-fm posi-traction
1966 Corsa Convert 180 wood wheel tele-column am-fm sport steering posi-traction
1965 Corsa Coupe Crown V8 temporarily red lined for repair
House Springs, Missouri

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Re: Carburetor backfire with rebuilt carbs
Posted by: Kamaka ()
Date: August 20, 2019 04:42PM

The saga continues. I swapped the original secondaries carbs back and took it for a ride - it won't idle down below 1000. I keep thinking vacuum leak SO I disconnect the balance tube, plugged the tubes in the head with rubber hose and bolts and checked the vacuum at each side. Right side 16-17 at idle which seems ok - the left side only 6! I pulled a valve cover and just checked to make sure no tight valves - all seems ok. I pull the exhaust off the left side wondering if I have a plugged system - nope still 6! Any thoughts? The engine runs fine but when it get s warm it won't run at all at idle and will stall - it does restart and then goes back to 1000 rpm

I still think massive vacuum leak - but where?

Any thoughts? What am I missing?

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