'89 Yamaha Ovation bogs when warmed up

I'm starting to work on my snowmobile getting it running for the winter. Last year when it warmed up it was bogging REALLY bad. It has some clutch problems (e.g, grooved clutch weights) and I was wondering if that's the cause or if I need to look at something else. (Note: I just restored this last winter, so i got the carb all cleaned/adjusted, so I'm sure its not that)
Edit: the bog is so bad that it nearly stalls with no passengers and it cant move at all on flat ground. It has to get...

'89 Yamaha Ovation bogs when warmed up