i have a 1999 300ex it has a cobra pipe and no other real mods it runs fine on the bottom end but once you gas it it kinda stalls and acts like it doesent want to go then it takes forever to get any speed wicth top speed for it this way is like 10-20 miles and hour i need to know whats rong with it so i can get it fixed thanks everyone

 

FIRST, on any 250X or 300EX with this problem, check to see if the choke lever is completely in the off position. Sometimes, the rubber fuel line going to the carb gets caught into the lever not allowing it to shut off enitrely.

 

yes that is one of the problems that they have.. maybe also bad gas or clogged jets.....