Really guys? Nothing?
I had a similar issue and it was the muffler. The baffles had rusted away and when running would actually block the exhaust when throttled. Just an idea, it sounded different, like when there is something against the back of the muffler and when I took it off it rattled.I have an o1' foreman 450 that runs great until it warms up then it loses power and barely runs. Once it cools down it starts right up and runs great until it warms up again. Would this be a bad temp sensor? Do these bikes have a limp mode? I've swapped out too many parts to list (including the carb) and I'm pretty much out of ideas for things to check. Btw the oil pump seems to be working fine.
Thanks, trying a different battery right now. Stay tuned. Lithium went dead after 45 minutes this morning.What I remember about the temp sensor on the older Honda quads was it only dealt with the oil cooler fan and warning light. No limp mode afaik. You need to determine if the issue is electrical or not. Checking for spark when it dies out might be easier said than done but could help.