I have a 1969 Johnson 20 hp that is driving me crazy. Went out a couple of weeke ago and it ran fine. About half way through the trip it got to where it would not get above idle while in gear. It would rev like crazy in neutral but not in gear. I have been told by several people that it sounds like a carb problem but I have removed, disassembled, cleaned and replaced the carb 4 times (that carb is cleaner that it was new) and still having the same problem. Any help would be great.