Originally Posted by DCalland
I am flying an RV-7A and am just under 700 hrs. of great fun. For the past 18 months or so I have had minor RPM fluctuations that are only at takeoff and climb settings. The first takeoff is pretty normal except over the 18 months or so the max RPM does not quite reach my 2650 limit as it used to. (I know I can adjust the max RPM but I'm after the bigger issue right now) After the engine is hot and I do a second takeoff I am getting RPM fluctuations of 50 to 200 RPM at takeoff MP and high RPMs. After I level and pull power and RPM back to cruise things are fine and the flight is normal. This has gradually worsened with time. I have a Hartzell CS HC-C2YR 74" prop and an MT governor which I just had overhauled 2 weeks ago. Lycoming O-360 A1A engine with standard mags. I had a friend with similar issues and his governor overhaul cured the problem. No so with me. I will have oil pressure of 82 psi in climb which is normal for my plane. The prop was bought new and has not been overhauled yet. No leaks that I can see. Engine runs great, clean oil, no ignition problems, and good oil analyses over the years. Hoping someone may have some insight here.
Does just your gauge change rpm, or do you feel/hear the fluctuations! If it is actually changing rpm, call MT and tell them that and they will put in a heavier spring (this used to be a common issue with the RV-10 with the MT governor). If itís just the gauge, then your sensor may be failing, or the resistor between your rpm pickup and the pleads is weakening so false pulses are coming through at high rpm.