Horse46 515 #1 Posted September 29, 2015 What are the causes for engine back fires?The engine runs fairly well, but back fires when closing the throttle.What is confusing is it was running fine before I took it out, I"ve done nothing to it, just bolted it back in Share this post Link to post Share on other sites
Tuneup 1,416 #2 Posted September 29, 2015 My experience has always been that a fast closed throttle will risk a backfire that can be eliminated if the exhaust is well sealed and the idle mixture is more on the rich side. Lean it out and get bigger pops. Richen it and you get more of a gurgle. The more open your exhaust is, the more risk is realized. You can also adjust your idle to reduce backfire. I recall that an increased idle helps. Share this post Link to post Share on other sites
Horse46 515 #3 Posted September 29, 2015 Hmm, that would make sense. I did back off the fuel as my old plug was quite black, and on checking the new plug it was also quite sooty. I guess a richer mix is better than a too lean one.I will have to have another tune up. Share this post Link to post Share on other sites
Tuneup 1,416 #4 Posted September 29, 2015 The list pros would have more to say but I would idle as rich as the plug would permit for extended idle to minimize backfire. You don't want those black plugs Share this post Link to post Share on other sites
C-101plowerpower 1,605 #5 Posted September 30, 2015 mine backfired a lot too, didn't really mind it tho, the neighbors on the otherhand did. i was using a straight tru pipe, when i switched to a decent muffler the backfiring decreased a lot Share this post Link to post Share on other sites
pacer 3,160 #6 Posted October 1, 2015 (edited) Yeah, one of the leading culprits in backfiring is often a leaky muffler/exhaust, especially near where the pipe comes out of the block. Did you remove the muffler when you removed the engine? Or if not did you maybe move it a bit? If it lost is seal and is able to pull air in, the excess oxygen mixing with the hot unused fuel leaving the chamber will ignite and ---- boom! Edited October 1, 2015 by pacer 1 Share this post Link to post Share on other sites
Horse46 515 #7 Posted October 1, 2015 Yeah, one of the leading culprits in backfiring is often a leaky muffler/exhaust, especially near where the pipe comes out of the block. Did you remove the muffler when you removed the engine? Or if not did you maybe move it a bit? If it lost is seal and is able to pull air in, the excess oxygen mixing with the hot unused fuel leaving the chamber will ignite and ---- boom! I did remove the it yes, I will check that, good point. 1 Share this post Link to post Share on other sites
