Wednesday I finally completed my weather delayed trip to Winter Haven from Buffalo in my Amphib Cub, somewhere about 1000 miles. The weather still sucks down here but at least the Cub is now safely tucked away.
About 20 miles from my final destination at 2000 ft, dodging storms and indicating 92 mph at 2400 rpm, the engine just slowed down on its own. First thing I checked was whether I bumped the throttle; nope, unchanged. The rpm wound down to about 2100 and indicated dropped to the low 70's. The drop took about 15 seconds. The sound was different and the vibration was more "coarse" but not really shaking hard. I've had carb ice in cruise in the past, also with an O-200, and the rpm change was pretty gradual and subtle, unlike in this case. Regardless, I turned on the carb heat. It was only on for 30 seconds but there was no change. I decided not to mess with the throttle as I was now only about 15 miles out. The good news is that this part of Florida has smooth/flat fields or nice round lakes.
Soon I had to reduce altitude to get under a cloud shelf and also get set up for landing. I did not reduce the throttle, just pushed the nose down. Of course the rpm increased some. Then after a few minutes of this decent the rpm increased to a normally expected level. Thereafter, throttle response was normal.
During this episode the EGTs and CHTs seemed normal as far as I could tell.
The oil was changed just before the trip with the addition of a little Camguard, I use 100LL.
What trouble shooting suggestions and in what order would you suggest?
Possible causes? I have an idea but would like to hear your thoughts.
Thanks,
Carl
About 20 miles from my final destination at 2000 ft, dodging storms and indicating 92 mph at 2400 rpm, the engine just slowed down on its own. First thing I checked was whether I bumped the throttle; nope, unchanged. The rpm wound down to about 2100 and indicated dropped to the low 70's. The drop took about 15 seconds. The sound was different and the vibration was more "coarse" but not really shaking hard. I've had carb ice in cruise in the past, also with an O-200, and the rpm change was pretty gradual and subtle, unlike in this case. Regardless, I turned on the carb heat. It was only on for 30 seconds but there was no change. I decided not to mess with the throttle as I was now only about 15 miles out. The good news is that this part of Florida has smooth/flat fields or nice round lakes.
Soon I had to reduce altitude to get under a cloud shelf and also get set up for landing. I did not reduce the throttle, just pushed the nose down. Of course the rpm increased some. Then after a few minutes of this decent the rpm increased to a normally expected level. Thereafter, throttle response was normal.
During this episode the EGTs and CHTs seemed normal as far as I could tell.
The oil was changed just before the trip with the addition of a little Camguard, I use 100LL.
What trouble shooting suggestions and in what order would you suggest?
Possible causes? I have an idea but would like to hear your thoughts.
Thanks,
Carl