my bike has no top end. i took carb off and completely cleaned. first and second and mostly third gear are ok, but when you get to 4th and 5th gear, it bogs down. no smoke. it maybe will go 15 mph in 5th gear. is it a ring and piston issue? how do i check without paying big money to have it fixed? i only use it for hunting and really dont wont to get rid of it as it has no real value. thanks for any suggestions