Quote:
Originally Posted by ROBERT JAM
I have a 1929 closed cab truck that has started back fireing thu the carb. Carb has been rebuilt and is in good condition. It seems to back fire after it warms up. Plugs are good, gas line is clear. Could it be a coil or coil wire? Any other trouble shooting sugestions would be helpful. Thank you.
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You are running lean.
That can be the GAV or a combination of the GAV and Idle mixture adjust setting! Do some adjusting.
If no success, hook up a vacuum gauge to the intake manifold at the windshield wiper connection point. The vacuum gauge should hold steady with the engine idling and should be running around 18 to 23. ( a good engine) and these numbers depend on altitude. The key is steady reading. If it is bouncing around there is a valve issue.