I agree that the symptoms do indicate a heat related problem, but like I said I ran this engine on the airboat numerous times without a bit of trouble.

I think I've solved it though. I downloaded the manual from Walbro for the HDC series carbs, and read how to set the metering lever. I took the diaphragm out and checked it again, and it's spot on where the manual says it should be. While I had the carb off and apart though, I took the high speed needle out and cleaned the passage out with carb cleaner. I noticed though when I took the needle out, it was set way to rich. (I counted the turns in so I could put it back to the same setting.) The manual said to start with both the high and low speed needles one turn out. Both of the needles on my carb were just over two turns out. So, I took the rest of the carb apart and cleaned everything really well, even though I didn't see any trash anywhere. I put it all back together and set the needles to one turn out, and went and started the engine. It ran well enough, and after closing the low end a bit and opening the high about the same, it's running great on the ground. I'm hoping to have time to fly it tomorrow and see how it does in the air. It looks promising though!

I'm guessing there must have been a piece of trash somewhere or something limiting the fuel getting into the engine, which is why the needles were so far open. It's running great now with the needles where they should be.

I'll be sure to update once I get it in the air!