38 Buick backfires through carb

[GSW38]

My 1938 special backfires through the carb at about half throttle. It does not backfire on acceleration. It only backfires on a steady half throttle.There is no backfire through the exaust.I think my springs in my carburator are weak but I am not sure.

Thank You

George

[Guest Straight eight]

Have you warmed up the engine to operating temperature, and set the tappets according to the manual reccomendations? Sounds like a tappet is set too tight

[Guest]

A lean mixture can also cause a backfire through the carb.

[GSW38]

Thanks Straight eight

I did run engine until it reached normal run temp and set valve lash to .o15 as my shop manual instructs. After this ajustment ther is no change the engine still backfires through the carb.

[GSW38]

I have not ajusted the carb air fuel mixture. I will do this tonight to see if this helps my problem.

Thank You

[sledheader 48381]

If you are talking about adjusting the screw or screws at the base of the carb I believe that is a idle only adjustment might want to check float level adjustment and internal passages[jets] for a restriction.

Don

[Gene Brink]

Did the same thing on a '64 Chevy pick-up w/283 V8 my dad owned years ago. Turned out to be a faulty distributor cap (tiny crack that filled with enough under-cap crud to conduct electricity to the wrong terminal so a plug would fire while an intake valve was still open). Idled just find but when the engine was running around 2500 rpm or so - pop, pop, pop...

Good luck.