My exhaust system backfires. it consists of headers, pipes, and mufflers. i have been told that the back fire in the exhaust system (not the carb) would be caused by air in the pipes because of poor welds. i have also heard that an H pipe is the correct way of exhaust work, instead of two isolated straight pipes.is either reason right? aftermarket carb, bypassing emissions controls, ‘84 305 K5 Blazer.
I own a shop, and have seen this for years. This is caused by the engine sucking air into the exhaust system via a leak. It can usually be found that the gaskets where the headers mount to the heads are leaking, and when you let off the gas it sucks air into the pipes, and explodes the excess fuel that is left over in the pipes. Replace these gaskets, and keep the bolts tight as in check them every couple of weeks. This is one of the drawbacks to cheap headers, as the mounting flange is too thin, and the bolts won't stay tight. As for the H pipe, they work really well. They do help scavenge the exhaust out of the other side as one side fires. Use a piece of pipe, and blow an air hose over the end of the pipe, you can see it form a vacuum on the other end of the pipe enough to suck stuff up into the pipe. This was invented by NASCAR way back in the 60's, and they found a scavenging pipe would increase the horsepower. Also by exiting the pipes at the side of the vehicle the wind going down the side of the vehicle would cause the same effect, and created more horsepower than running them out the back straight. Some people will use a turn down on the ends to capture air flowing under the vehicle, but it's just not the same. One more thing; The backfire can and will sometimes burst the muffler, as I have seen it blow a huge hole in them right at the seams. Glad to help out, Good Luck!!!
