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Bad engine running, misfire and rpm drop

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Joined
Jan 23, 2022
Messages
24
Reaction score
3
Location
Germany
Dear Specialists, I need your help.

My Acrosport II is equipped with a Lycoming O320 E2A, Marvel Schebler carburetor MA 4… and Slick magnetos 4370 and 4373.
Last Time the Engine has rpm drop during magneto check and misfiring at low load.
I did a lot of things to fix the problem:
-overhaul magnetos -both had very bad internal timing bat it was not the problem
- change spark plugs
- check the ignition harnes
- seal the crankcase
- change the rubber tubes at the intake manifold
- check the gaskets at the intake
- clean the carburetor
- measure the pressure difference (leaktest)
- look into the combustion chaber
- check the valves from outside

After installing an engine monitoring system I found that Cylinder 3 does not fire at low load (e.g. ideling or descends).
At full load all cylinder are firing. During leaning cyl 3 goes very hot.
It seems tat it runs lean.
The Leaktest show s very good values for cyl 3.(5bar/4.95bar) The worst value has cyl nr. 1 (5bar /3.9 bar) but it works pretty good?

If somebody could give me an advice?

Best regards Mathias
 

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