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IO-360 Backfiring

R

RV8FLYR

I'm New Here
I have a Lyc. IO-360 in my RV-8. Occasionally after the engine is warm, and idling, I get some backfiring. I'm idling between
800-900 rpm. I have tried checking the security of the intake tubes. Made sure the Bendix injectors are cleaned and free-flowing.
Pulled back the mixture during taxi to prevent load-up. I have the Van's stock exhaust stacks. Also, using a Whirlwind 3-Blade
Composite Prop. Any thoughts ???
 
Is it truly a backfire (which is coming out of the intake)? An actual backfire will often times damage the air filter. Or is it just a pop or a miss? Does it go away if you lean or enrichen the mixture?
 
Is the engine otherwise smooth? Sometimes you can get unburned fuel in the exhaust light off if the ignition is incorrectly timed, or missing or something.
 
Mine does that too after landing when it's hot and after taxiing for a while. I attribute that to fuel boiling in the spider and nozzle feed lines, causing mixture in the individual cylinders to alternate rich/lean. The popping in the exhaust is when that cylinder, on that particular combustion cycle, was too lean (or rich) to fire and the fuel lights off in the exhaust instead.

It's the same process which makes every hot start a flooded one on Bendix-style fuel injected engines.

You can play with the throttle and mixture to improve the popping a bit when it's happening.
 
D-Dubya said:
Is it truly a backfire (which is coming out of the intake)? An actual backfire will often times damage the air filter. Or is it just a pop or a miss? Does it go away if you lean or enrichen the mixture?
Click to expand...
Thanks to everyone for the very timely replies. I'm not sure of the forum's protocols, but if I reply to you. does it go to all that
have responded to my initial question ?
It is a loud pop out of the exhaust stack and I believe it to be almost a white puff/pop. This A/C was initially certified in 2005
and it is a low time engine. The white color leads me to a raw fuel issue but I'm not sure where to go from here.
 
walkman said:
Is the engine otherwise smooth? Sometimes you can get unburned fuel in the exhaust light off if the ignition is incorrectly timed, or missing or something.
Click to expand...
Thank you for the timely reply. Engine is idling smoothly and both Slick mags are right on timing.
 
hgerhardt said:
Mine does that too after landing when it's hot and after taxiing for a while. I attribute that to fuel boiling in the spider and nozzle feed lines, causing mixture in the individual cylinders to alternate rich/lean. The popping in the exhaust is when that cylinder, on that particular combustion cycle, was too lean (or rich) to fire and the fuel lights off in the exhaust instead.

It's the same process which makes every hot start a flooded one on Bendix-style fuel injected engines.

You can play with the throttle and mixture to improve the popping a bit when it's happening.
Click to expand...
Thank you for the timely reply. Folks have told me that this issue is a normal one for RV's and this engine. That doesn't sound
normal to me. I'm thinking maybe an injector/spider issue.
 
Not normal IMO, I've had everything from carbs and FI (AFP now) with all types of electronic ign and mags, and never had back fires.
Stumbling when hot yes, but no back firing ever.
 
Sounds more like an after fire (smoke out the tail pipe is the indicator). I suggest:
- Mixture way too rich when idling. You should lean almost to cutout. If the engine stumbles when advancing the throttle for taxi you are about lean enough.
- Timing not quite right.

Carl
 
I don't think you can properly diagnose this issue, if one exists, without first determining if it truly is a "backfire", or is unburned fuel lighting off in the exhaust, or is a "lean pop" or something else. I'd recommend finding someone local who can help you with outside observations while you operate the engine to cause the potential problem. Maybe even record the event and share here
 
walkman said:
I don't think you can properly diagnose this issue, if one exists, without first determining if it truly is a "backfire", or is unburned fuel lighting off in the exhaust, or is a "lean pop" or something else. I'd recommend finding someone local who can help you with outside observations while you operate the engine to cause the potential problem. Maybe even record the event and share here
Click to expand...
To illustrate this point, and maybe a little chuckle to the thread, I recently (this week) had a similar problem. I had just replaced my throttle and mixture cables, cleaned and gapped my plugs, and cleaned my fuel injectors. On starting for post-work testing it was very difficult to start and once started I was getting MASSIVE popping and banging, and actual backfires (enough to destroy my airbox). A couple of days of wracking my brain, what on earth did I do that could have made that much of a change? It turned out that in that blind area behind the panel where you thread the control cables through by feel I had managed to swap mixture and control! doh!
 
Sometimes loose exhaust connections will cause after fire. Leaky or blown exhaust gaskets, loose exhaust nuts, loose slip joints and very short stacks are often culprits. Also these items may make it pop on throttle reduction.
Good Luck,
Mahlon
 
mahlon_r said:
Sometimes loose exhaust connections will cause after fire. Leaky or blown exhaust gaskets, loose exhaust nuts, loose slip joints and very short stacks are often culprits. Also these items may make it pop on throttle reduction.
Good Luck,
Mahlon
Click to expand...
Always worth putting a spanner on the nuts (heh heh) and replacing any gaskets suspect or where there's indication of an exhaust or intake leak.
 
I had a similar issue in my Long EZ with a carbureted O-320. Turned out to be a loose intake pipe. May not be applicable on an injected engine, but it is quick to check.
 
I had a similar sound (maybe?). Chased for long while. After installing a 4 point engine monitor I found that the EGT / CHT in one cylinder was way different.
Cause? Small spec of crud in the fuel spider.
Making one cylinder very lean at idle.
 
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