My 300EX will run fine all day except maybe 2 or 3 times a ride I will have trouble. I leave it on reserve because it is usually after landing on a jump and taking up speed again so I figured fuel could be sloshing away from fuel valve. However, this doesn't fix it all the time, I can have a full tank and be on a hill climb and it will bog once but not again for a long time. When it bogs, it is only above about 3/4 throttle. Is there a high idle vent that could be plugged or a jet I could clean easily?

 

Actually what the problem is, is fuel slosh inside the carb. Have you had the carb dis-assembled? if not you might want to remove the bowl from the carb and see that the anti slosh piece is in place, it is a plastic thing that looks kinda like a hat that goes over/around the main jet.