Rookie
Registered User
WA
Saturday, I flew my O-320 powered Super Cub to Oregon, seeing about 2500 RPM at max throttle, along the whole way. I'm still learning about this plane, and this was my longest cross country flight in this plane to date, flying about 2 hours. I flew at 5500', and although I kept pulling the throttle back to bring down the RPMs, pretty much every time I stopped looking at the tach, I crept back up to 2500 RPM (I must be a bit ham fisted).
Anyhow, yesterday when I began the trip home, all I could get was 2200 RPMs. I flew to KLS, then OLM, but even after carb heat, max throttle only got 2200 RPMs. During the run up, the mag drops were normal, and carb heat operated properly. I decided to hope that it had something to do with the rain, and I did clear a bit of carb ice once, so maybe the 'at-mo-fere' was doing something I thought... I had to leave the plane at OLM because of weather, and when I brought it home today under a broken sunny and dry sky, I still couldn't get more than 2200. I'm starting to think something is probably wrong.
When I got home, I started to chat with the local mechanic Phil. He had some suggestions, but seemed too busy to have a look. He loaned me an electronic tach (thanks Phil!) and my mechanical tach checked out, max I got it to read electronically was 2250 RPMs. Phil suggested I examine the carb to verify that it was hitting the full throttle stop; it was. He also said I should verify no obstuctions on the air filter; I didn't take it apart, but nothing seen.
This engine has an undesireable history. Although it has only about 400 hours on it, it entered service (with the rest of the plane) in 1980. The plane worked herring spotting on floats in AK for three years, before being damaged in a wind storm in 1983. In 1985 it was brought back to Washington State on a fishing boat. It was a project from 1985 to 1995 (replacement wings, fuel tanks, struts, etc.), and it was signed back into service in 1995 at about 320 hours. An almost immediate prop strike incident resulted in the engine being torn down, and having a bunch of service (including an AD), which has been described to me from the minimal documentation, and the reputation of the involved parties, as prudent. I'm inclined to believe that. I have been told that the crank was sent for magnaflux inspection, and checked out good. The minimal documentation seems to support this. After the prop strike, the previous owner operated it about 20 hours one year, 10 the next, 5 after that... When I bought the plane a year ago, it only had 40 hours on the rebuild after six years. Poor little neglected Super Cub!
I've put about 50 (tach) hours on it in the last year. I'm planning on flying more, but I was somewhat limited by availability of my instructor before I got my conventional gear endorsement. As far as I can tell, it's been operating fine, this is the first strange thing I've been able to detect.
Compressions on the last annual, in May, were "1-72/80, 3-75/80, 2-75/80, 4-75/80".
I was leaning at 5500' during the cruise down to Oregon. I still need to verify the mixture control hasn't slipped (it seems fine, and some leaning at cruise did seem to get an RPM rise, indicating rich of peak).
I'm calling my regular mechanic, but anyone want to take any guesses? Check the compressions again? What could cause a 300 RPM reduction in max throttle overnight? Can my carb do something like that internally? Slipping butterfly? Sticky valve?
Oh yeah, and by the way. Why was the overflowing 100LL dripping out when I was testing the throttle linkage bright red, rather than blue?
Anyhow, yesterday when I began the trip home, all I could get was 2200 RPMs. I flew to KLS, then OLM, but even after carb heat, max throttle only got 2200 RPMs. During the run up, the mag drops were normal, and carb heat operated properly. I decided to hope that it had something to do with the rain, and I did clear a bit of carb ice once, so maybe the 'at-mo-fere' was doing something I thought... I had to leave the plane at OLM because of weather, and when I brought it home today under a broken sunny and dry sky, I still couldn't get more than 2200. I'm starting to think something is probably wrong.
When I got home, I started to chat with the local mechanic Phil. He had some suggestions, but seemed too busy to have a look. He loaned me an electronic tach (thanks Phil!) and my mechanical tach checked out, max I got it to read electronically was 2250 RPMs. Phil suggested I examine the carb to verify that it was hitting the full throttle stop; it was. He also said I should verify no obstuctions on the air filter; I didn't take it apart, but nothing seen.
This engine has an undesireable history. Although it has only about 400 hours on it, it entered service (with the rest of the plane) in 1980. The plane worked herring spotting on floats in AK for three years, before being damaged in a wind storm in 1983. In 1985 it was brought back to Washington State on a fishing boat. It was a project from 1985 to 1995 (replacement wings, fuel tanks, struts, etc.), and it was signed back into service in 1995 at about 320 hours. An almost immediate prop strike incident resulted in the engine being torn down, and having a bunch of service (including an AD), which has been described to me from the minimal documentation, and the reputation of the involved parties, as prudent. I'm inclined to believe that. I have been told that the crank was sent for magnaflux inspection, and checked out good. The minimal documentation seems to support this. After the prop strike, the previous owner operated it about 20 hours one year, 10 the next, 5 after that... When I bought the plane a year ago, it only had 40 hours on the rebuild after six years. Poor little neglected Super Cub!
I've put about 50 (tach) hours on it in the last year. I'm planning on flying more, but I was somewhat limited by availability of my instructor before I got my conventional gear endorsement. As far as I can tell, it's been operating fine, this is the first strange thing I've been able to detect.
Compressions on the last annual, in May, were "1-72/80, 3-75/80, 2-75/80, 4-75/80".
I was leaning at 5500' during the cruise down to Oregon. I still need to verify the mixture control hasn't slipped (it seems fine, and some leaning at cruise did seem to get an RPM rise, indicating rich of peak).
I'm calling my regular mechanic, but anyone want to take any guesses? Check the compressions again? What could cause a 300 RPM reduction in max throttle overnight? Can my carb do something like that internally? Slipping butterfly? Sticky valve?
Oh yeah, and by the way. Why was the overflowing 100LL dripping out when I was testing the throttle linkage bright red, rather than blue?
