Back firing on power to idle. Lycoming 540 Edition

SixPapaCharlie said:
Only recently noticed this but I started hearing a pop or two a few months back upon pulling the power on short final.
I don't recall it happening in the past. I "think" it is that cool pop pop pop backfiring that I hear all the RV pilots doing when they do their overhead break to power off 180 and I hope it sounds cool to people on the ground.
Maybe they hear it and Go "Oh I am going to look up and see what RV is making that cool sound" Then they look up and it is a Comanche and they are even happier because Comanche!

But historically it didn't do it. And now pretty consistently when I pull power on final I hear the a pop or 2.
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Ignore it, hot pipes igniting small amount of gas vapor in the exhaust probably
 
Well, something changed if it only started in the last few months. If it wasn’t pilot technique, then it’s a mechanical deviation that should be assessed “to make sure it’s nothing”.
 
Sac Arrow said:
Backfire on decel is caused by unburned fuel igniting in the exhaust, which would be aggravated by an overly rich mixture. I personally don't enrichen at all unless I'm descending from a high altitude. But I also generally run LOP in cruise as well.

What are you flying? A Bonanza? Presumably something with a constant speed prop. Add power, mixture prop throttle. Reduce power, throttle prop mixture.
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That's an after fire.
 
Can a leak in the exhaust manifold lead to backfiring when pulling the throttle?
 
NoHeat said:
Can a leak in the exhaust manifold lead to backfiring when pulling the throttle?
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I wouldn't think so. There is still a positive pressure in the exhaust manifold.

As a side note, there was a popular emission control device in mid 70's cars called the AIR (air injection reaction) system. It injects air from an engine driven compressor in to the exhaust manifold to aid the catalytic converter. This was back when engines still had carburetors and mixtures ran rich. There was a check valve that would stop the flow of air during deceleration in order to control backfiring. The one in my Isuzu pickup quit working, so I just disconnected the AIR system all together and life was good.
 
Sorry, I haven't read all this thread...........and I'm sure it has been brought up. But popping on throttle pull means an induction leak. I'd replace all the seals.
 
Might have found a culprit. last year, we got all new gaskets / hardware for the intake tubes.
I spoke to my mx and he said "Double check the hose clamps on the intake tubes, the rubber shrinks and those can become lose."

I was able to get 2 full turns on all 12 of the hose clamps. Took it around the pattern twice. Once full rich and once leaned a bit and no backfiring.
Not calling it yet but when the weather improves, I am going to do some more flying and see if that might have been the issue.
 
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