Model a backfire

[tony1]

Need a little help my car backfires when i rev the engine but if i pull the choke almost closed it revs good and no backfire. any input would be appreciated. I have tried adjusting the gav. What puzzles me is when i cover the carb or pull choke almost closed it runs good not sure if carb or firing problem. Thanks Tony.

 

[Curtis in MA]

Mine was from rust in the gas tank. Put in a tank filter and it was fine.

 

[tony1]

I have done all of that. The fuel is clean Thanks

 

[ryanheacox]

Very leaky manifold gasket causing a lean condition?

 

[tony1]

Does not seem to have any leaks.

 

[Curtis in MA]

While running spray starter fluid around manifold.

 

[tony1]

I will give it a go. Thanks

 

[Tudortomnz]

Clean out [compressed air] all jets. Check timing & make sure you have the gav. no more than quarter open when warmed but not closed right off. It appears to be too lean. Cheers- Tom.

 

[ryanheacox]

Was also wondering about plugged jets but didn't know if it would give the symptoms described.

 

[100IH]

Don't think with your wallet! We all do that until you realize how much time is wasted.. If you suspect a vacuum leak, put a vacuum gauge on it. Should be around 16-17 in/HG. If you suspect too lean squirt some fuel (gasoline, ascetlyene, propane, ether). Now compare which one has a bigger effect.Good to know stuff. Now add one of the fuels around the intake manifold. This shows you where. Listen for the engine to pick up RPM and watch the vacuum correction. A piece of 1/2 inch heater hose about 2 1/2 feet long is great for hearing where there is a leak. These 2 problems are interdependent on each other.

 

[tony1]

Hi i took the carb apart and cleaned it still same thing. I guess the distibutor is next but it has that waffle manifold and a little heat plate so not sure id i can get the distributor

out if i need to without pulling manifold hope not.

 

[1931 flamingo]

Did you DO what was posted in #6 and #10 above???
Paul in CT

 

[tony1]

Not yet but going to tommorow. Thanks

 

[tony1]

Where do you hook up the vacuum gauge?

 

[ryanheacox]

The wiper port on the intake manifold if you have one

 

[Benson]

If vacuum wiper ... remove line at manifold and plug see it still fails....

 

[tony1]

I think there is a plug there. I will try it.

 

[eagle]

Sure sounds like a leaking manifold gasket. Id take a propane torch, on but unlit, and run the propane around the gasket. You'll hear right away when you get to the leak.

 

[Purdy Swoft]

Several things can cause back firing . Check points gap and initial timing . Improper float setting ,, GAV closed too much and vacume leaks anywhere from the intake manifold to the vacume windshield wiper motor when present will cause a lean condition . Any flow restriction from the gas tank to the carburetor also causes lean operation .

 

[tony1]

I appreciate all the responses i am going to try some of them today and tomorrow. I did set the points which were real close and pulled fuel line from carb good flow. There is no wipers just a plug in manifold. I do suspect maybe carb float i took it apart and the catch when the float drops was bent letting float drop all the way down and i am not sure about that valve in there. I will keep you posted on out come Thanks again Tony.