The plane is an Tower Hobbies Uproar that I put on floats. I didn't think about taking off the spinner before I removed and replaced the engine with another that I had. I raced it around the yard on the floats and it does just fine, but as soon as I get it in the air and up to mid throttle speed, it starts to run irratically. Kind of a off-on-off-on thing going on. Here is a picture of the model hanging in my garage.

I think it was right here on RCU that I saw the other thread, and it left everybody baffled. The thread starter knew what the problem was before he posted but wanted to make it a guess what the problem is thread. It had everybody stumped. He then said that changing the spinner solved the problem completely.