DrBill Posted March 9, 2015 Report Posted March 9, 2015 The last 2 landings I noticed a backfire when I pulled the throttle back on final. Was running around 1700 rpm and pulled back to idle.. .BANG. Got the mechanic on it today and we leaned out the idle a bit seemed to help but I can still make it do it bringing the rpm up to 2000 then smartly back to idle. Not every time but 4 out of 6. I can lean it out more and make it stop but then it runs rough near 2000 and if I enrichen to smooth out at 2000, the backfire will come back. Any ideas ? Bill Quote
chrisk Posted March 9, 2015 Report Posted March 9, 2015 I flew a F model that did this. When we pulled the cowling, the exhaust was not properly connected. --It was some time ago (and not my plane), so I don't recall all the details. I have no idea why this would have caused the backfire. In any case, it's something to check. Quote
Wesley brown Posted March 9, 2015 Report Posted March 9, 2015 During low rpm settings and the engine cfm being low as well it will have the tendency to load up and backfire by burning excess fuel. My plane does this if I pull to idle on landing and especially with carb heat on. I lean a tad during landing if I hear it a little and it takes care of it. With carb heat on it always does it. Check timing and lean you idle settings according to the service manul. Also check your carb heat box! If it is sloppy it can lead to hot gasses bypassing the butterfly causing a hot/rich issue. You wouldn't believe how many carb heat boxes aren't correct, killing speed and mixture issues. Quote
Bob_Belville Posted March 9, 2015 Report Posted March 9, 2015 During low rpm settings and the engine cfm being low as well it will have the tendency to load up and backfire by burning excess fuel. My plane does this if I pull to idle on landing and especially with carb heat on. I lean a tad during landing if I hear it a little and it takes care of it. With carb heat on it always does it. Check timing and lean you idle settings according to the service manul. Also check your carb heat box! If it is sloppy it can lead to hot gasses bypassing the butterfly causing a hot/rich issue. You wouldn't believe how many carb heat boxes aren't correct, killing speed and mixture issues. Bill has an E. Fuel injected, no carb. Quote
clh Posted March 9, 2015 Report Posted March 9, 2015 Backfires can occur whenever you have excess fuel in the exhaust. This could be as simple as not good atomization by the fuel injectors at low flow. The loose exhaust above was likely caused by the backfire. I has some popping when I quickly pulled to idle a few years ago. Cleaning the injectors and the spider appeared to clear it up. Quote
stevebennett327 Posted March 10, 2015 Report Posted March 10, 2015 Mine was popping like crazy, A previous post or two said unburned gas in the exhaust. I took off my cowling and found a big hole in the exhaust. I ordered a new exhaust system and problem solved. Plus it's quieter, and doesn't stink "as much". Shouldn't the exhaust last more than 51 years ? Steve Bennett 64 E model Quote
DrBill Posted March 10, 2015 Author Report Posted March 10, 2015 I just put a new exhaust on in October ! We're (mech and I) are thinking fuel injection problem, perhaps hard/dry diaphragms. We're going to play more tomorrow, perhaps clean the injectors. BILL Quote
StinkBug Posted March 10, 2015 Report Posted March 10, 2015 I noticed a similar issue yesterday, though in a pretty different situation. I was flying up around 11,000' and decided that since I needed to descend anyways I'd test out the glide performance, so that I'd be familiar if I ever need it (hope not). Anyways, if I pulled the throttle ALL the way out I got quite a bit of coughing and backfiring, even while still leaned. Since this isn't a normal situation, and I wasn't doing it for long I'm not worried about it, but it was interesting. As a side note, it's pretty amazing how much of a difference the prop setting has on glide. At 100mph with the prop all the way in I was dropping almost 1000fpm. With the prop all the way out I was around half that. Could have gone pretty dang far gliding from that altitude! Quote
Wesley brown Posted March 10, 2015 Report Posted March 10, 2015 Bill has an E. Fuel injected, no carb. Oops sorry I was reading on my phone. Seems like the suggestion of fuel injection system and exhaust is a good answer. My friend at my airpark has a E. When he first purchased it he had popping and it was the exhaust but on take off. After he changed it all was well. People heard the popping on the ground we never heard it In the cabin. Quote
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