Low Engine RPM

[allanrbowman]

I recently purchased a PA22-150 that on a run up or takeoff will not exceed 2400 RPM. The POH shows 2700 RPM. The mag drops are OK and the engine runs smoothly. Throttle goes from stop to stop. Removed, checked and cleaned plugs (they were nice light brown tan) , tested mag leads (fine) all resulting in no change in operation or top RPM. Tach checked OK using laser tach so it's not reading incorrectly.

Prop is Sensenich M74 DM-0-60.

The only other information I have is that on a 300 mile trip, at 6500 ASL, with the engine leaned, fuel consumption was 8.5 GPH which seems high. Since there was no fouling or blackening of the plugs, I'm guessing that the consumption is normal although high compared to the POH.

Can anyone offer suggestions regarding the inability to achieve the POH RPM of 2700?

Thanks, Allan

[JohnW]

Allan; with a fixed pitch prop, an engine will not turn to redline statically on the ground. The Type Certificate Data Sheet sets the minimum and maximun allowable rpm (at WOT, static, on the ground) for the PA-22 -150 at NOT OVER 2450 or NOT UNDER 2250 for the Landplane with a M74DM installed. Looks pretty much like you don't have a problem, don't it? Very few airplanes will make redline even in LEVEL FLIGHT with the throttle wide open "forever". The redline is the MAXIMUM RPM that engine is supposed to be turned, and as long as you are within static limits from the TCDS, you have an acceptable pitch M74DM installed. It IS quite possible to turn OVER REDLINE with the nose down. The engine will likely NOT "explode" if that does happen, but Lycoming sets the redline with serviceability and longevity considered.

[Steve Pierce]

Looks like normal static and take off rpm to me, especially considering your prop pitch. Fuel burn looks dead on also. You have a cruise prop and it will generally turn a little less rpm static as a climb however it looks like a good static rpm to me.

[allanrbowman]

Thanks gentlemen, the best problem is no problem at all.

Allan. :)