50cc dies to 10mph when engine hot

[skyrider]

The previous "bogging" fuel issue happened with the engine full to 3/4 full, not overfull though. Yesterday I did a the very hard test ride (with the cap tight) that I previously did with just 1/4 tank left and no deceleration problem. There is an overflow hose just below the gas cap and that is clear, so perhaps that acts as a type of vent. When I fill it I'll do another test ride with the cap lose and see what happens. The fuel line doesn't seem to be pinched.