912 100 hp with 700 hours
Last week I taxied out to the runway. After I did the run-up the engine started running really rough. Like on two cylinders only. Barely made it back to the hanger. The next morning it ran fairly well except the mag check was really bad. Drop 300 rpm and misses. Replaced the spark plugs and ignition wire caps and the mag check is good - 100 rpm and smooth. There still seems to be a problem. At 4000 rpm the tach needle slowly wonders back and forth about 50 rpm.

Temp was about 30 F when the rough running occurred. Could water in one of the fuel lines have frozen? (not carb ice)

Any suggestions on the sudden super rough engine and/or the tach wondering?

Carb is balanced
New carb floats

  • Re: Engine runs rough

    by » 6 years ago

    My engine did that a while back and wound not correct. Just before the run-up I got a high fuel pressure alarm. Could not find the problem so I called Joe at Lockwood Aviation and he had me check the slider in the carburetos and they were stinking not moving freely. Most lickly caused by the flooding due to high fuel pressure. Cleaning and lubing fixed the problem.

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