Backfire

[BIGUNDIES]

Hi

I have a 350 Chevy with a holley carb. When I run my engine at 2000 revs or above for more than a second, I get a popping at the exhaust (Backfire). If I just rev the engine ie, press the accelerator for a short time then I don't get the problem. Any ideas what can cause this? It also seems to get worse the hotter the engine gets.

[robert]

Are you sure its a backfire, or is it a small popping sound. Backfires are very loud, however it sounds to me like it is either unburnt fuel, or you have a air leak on the exhaust somewhere.

Look for the air leak first at the exhaust joints, if you can't find one, then it will be unburnt fuel.

[BIGUNDIES]

Hi Robert

Thanks for responding to my post. Its a small popping sound from the exhaust and not a load bang. If it is an air leak in the exhaust system, would this give me problems on my emissions tests?

[robert]

Originally Posted by BIGUNDIES

Hi Robert

Thanks for responding to my post. Its a small popping sound from the exhaust and not a load bang. If it is an air leak in the exhaust system, would this give me problems on my emissions tests?

That depends on the block being used. If it is an old block, then its visual only.

Did you seal the joints with any sealant?

[BIGUNDIES]

Hi Robert

I have a 1983 block so I'm alowed 4.5 on the co2 and 1200 hc at 2000 revs. I didn't put any sealent on the exhaust system where the main side pipes connects to the four down pipes. I was told not to do this because I'm stripping the car down after SVA for painting. When I did the emissions test at the SVA the drivers side passed with 4.45 co and 500 hc at 2000 revs. The passenger side failed with 2.89 co and 2200 hc at 2000 revs. The passenger side was popping which the examiner said was caused by the engine not running properly. The engine never popped or made a sound in the past, it is only since we had to lean out the mixture dut to the co2 being around 10 when we started.