Rough engine at low RPM
 

I had problem like yours. I have a normal asperated 337H that would run rough at low rpm and would just die out on some landings, that was 5 years ago. I took it to a old O2 mechanic
from Vietnam and he fixed my problem after having it to 3 other shops. He put a set of gauges on the fuel pump outputs and ran them back to the pilot seat to watch at differant RPM and adjusted the high and low pressure output at the pump. That solved my problem. I have flown my 337 for 5 years and all is now fine at all RPM. He worked out of Bloomsburg, Pa. the last I knew. Dale Campbell

You can go to the TCM website and download the TCM Service Bulletin 97-3b. It explains all of the fuel setups like your good mechanic accomplished!

Setting the low pressure reading to the bottom of the low-pressure range and high pressure reading to the top of the high-pressure range seems to give excellent results.

sometimes when the pressures are correct and it still runs rough, look for leaks, these planes are old and a lot of "o" rings are getting very hard and loosing sealing abliity, sucking air can show up as fuel stains. at higher settings an abundance of fuel is flowing into the system thereby making the leak/sucking air of little consquence. however at reduced power settings they can make a substanial impact as the quanity of fuel flowing in the system as it is much lower allowing the leaks/air sucking to super lean or starve it till it quits

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See you in Key West.......

Running Rough
 

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Rough Engine
 

Roger. Copy that.

Big AL is right. Leaks whether fuel or air WILL cause these symptoms. If it's leaking either, it's no longer a conforming engine. Non-conforming engines don't run as well as conforming ones! <g>