acceleraton lag

[davisX500]

Yesterday I took out my 250 scooter . Everything seemed fine for the first three miles I drove (which is a gravel road) then once i got to the black top she would only do about 50 mph i kept up this speed while toying with the throttle and all at once boom she kicked in and i was doing 90mph yes i said 90mph . so i thought addjust the throttle cable which was loose as i found out but didnt solve the problem. any ideas? i was told check the accelerator pump but have no idea how to know if its bad . well it seems to kick in as soon as i hit 50 mph on the dot. I am soooo lost.

[davisX500]

since I have posted this I have (changed the oil adjusted the slack out of the thottle cable and looked at the accelerator pump as I dont know much about it it does seem to function properly.) all of these have helped but not resolved the problem.

[ce]

check the vacuum diaphragm in the top of the carb imay have a holeand it won't lift the slide all the way up.

Look at the exploded diagram at stadium yamaha, a Kymco parts supplier.

[BigOrange]

I had the same problem.  What CE said! It is the diaphragm and the piston mechanism in the carburator .