As I get up to cruise at 4500 i try to take some power back, but I pull the cable about all the was and only loose 3-4" of manifold pressure. And when I take it further it makes a weird humming noise (similar to the stall warning horn sound but not as pronounced.) So I figure I should leave it be until I am on top of the next airport to land on. I get over a familiar airport nearby with large runways and decide to remove power. And so I pull power to what should be idle, only comes down to like 18mp which in an old mooney doesn't do much to help you get down/slow down. Also the engine was running pretty rough, I had the carb heat on. So I finally got it down to pattern level and get the gear down get ready to pull the mixture and silence......Glided in really smoothly and set her down 1/3 down the runway.
After coasting to a stop we realize this is way to far to have to push the plane to the ramp ! So we turn it back on and it roars back to full power and they only effect I have is to turn it off.....
It was about 8-10 degrees F OAT on the ground....So who's got guesses ? I have my ideas but am curious to see what other think or have had this experience. It was dark and f-ing cold out so we didn't bother taking the cowl off, my mechanic will be looking at it tomorrow. Pretty weird glad it was too much power vs. the opposite !
Mike

