msouers

Hello,

I fly a TF T-34 Mentor which weighs about 15 pounds with a OS 120 Surpass III for about two years now. Just in the last month I am losing alot of power, barely able to get off the ground for takeoff. My tach says 7600 RPM with a APC 16x8 prop. The valves are adjusted, new F plug and the engine idles and transitions to full throttle very well. Something has change because around July and August I had good power takeoffs. The colder weather or new fuel (bad fuel?) could be the problem? Any suggestions would be greatly appreciated. Thanks!

Mark

Bax

My Feedback: (11)

Did you readjust the high-speed needle? With colder air temperatures, you will have to richen the engine because the air is more dense. The needle setting you used all summer will now be too lean.

Please remember that the high-speed needle needs to be properly-adjusted before EVERY flying session because it will change as the weather changes.

If your needle adjustment doesn't help, then you may have an engine that's starting to lose compression due to age, a lean run, foreign object ingestion, and so on. It may need a teardown to check.

msouers

Bax,

Thanks for the response. I am going to try an APC 15x8 prop to see if I can get 9200-9500 RPMs. What should be the average low idle RPM? I am getting about 3400 RPM. Thanks for your time.

Mark

Bax

My Feedback: (11)

We find that any RPM below 2,300-2,500 is "good" for idle. The lower, the better, but we must maintain good throttle response. Idle is the first thing to go bad when the compression is starting to go for whatever reason.

msouers

Bax,

Thanks for the input again. I am going to try the APC 15x8 prop. This teardown that you mention, what does this involve? Is this something that I or an experienced friend could do?

Mark