Very odd phenomenon - could use some help/ideas from the group.
Engine is a carbureted O-320-E2G (150 HP) on an RV-4. SMOH is about 1400 hours.
Engine starts right off. Run-up is fine, mag check excellent. Take off and climb-out is normal - engine runs very strong. Runs great for several flights/several hours, but eventually I notice the CHT on #3 is looking cold. I don't have an engine analyzer, so the temp on #3 is all I have to go on. After another 10 minutes or so the CHT drops away almost completely and the engine starts running rough - engine seems to be flaming out (for lack of better words). Make a beeline for the airport and hope it doesn't quit. Dangerous and nerve-wracking.
I'll take the plugs out or a good cleaning. Reinstall them and the engine runs fine again, but after a few hours the problem comes back again.
Compression of very good (high 70's). Borescope doesn't show anything abnormal. Plug resistance are all at out 1000 ohms - good readings. I'll check the timing later today.
Lots of acro flown, so carb does see zero-G a few times each flight. Thinking maybe a faulty carb. Hate to exchange it if it's not the cause.
Any help/ideas appreciated.
Engine is a carbureted O-320-E2G (150 HP) on an RV-4. SMOH is about 1400 hours.
Engine starts right off. Run-up is fine, mag check excellent. Take off and climb-out is normal - engine runs very strong. Runs great for several flights/several hours, but eventually I notice the CHT on #3 is looking cold. I don't have an engine analyzer, so the temp on #3 is all I have to go on. After another 10 minutes or so the CHT drops away almost completely and the engine starts running rough - engine seems to be flaming out (for lack of better words). Make a beeline for the airport and hope it doesn't quit. Dangerous and nerve-wracking.
I'll take the plugs out or a good cleaning. Reinstall them and the engine runs fine again, but after a few hours the problem comes back again.
Compression of very good (high 70's). Borescope doesn't show anything abnormal. Plug resistance are all at out 1000 ohms - good readings. I'll check the timing later today.
Lots of acro flown, so carb does see zero-G a few times each flight. Thinking maybe a faulty carb. Hate to exchange it if it's not the cause.
Any help/ideas appreciated.
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