[Ozark-al]

I think we can all agree that this is an air leak of some kind. It seems that you would have to run with the filter off to get sand in the motor but that is a possibility. It sounds like your on the right track checking the engine for sand and checking for air leaks. Don't give up on Nitro, just have a brushless system for backup like me when I get fustrated with Nitro. Good Luck.