i recently put a 300ex carb on my 250x and i changed out the pilot screw from a 250x carb onto my 300ex carb. i can only start it when the choke is on and it idles fine with the choke ON. when i take the choke off it dies unless you really give it alot of gas. i took the spark plug out and its carbon black (getting to much gas) and there is white on there too (getting to much air). is my problem that i need a smaller main jet?

 

is there any other mods and what is the main and slow jet sizes? sounds like it cant handle the fuel load,let me know....

 

250x main jet is 125 and slow jet is 35, 300ex main jet is 122 and slow jet is 38 and there are no mods except the new wiseco piston not bored.

 

make sure your needle is set all the way to the lean setting and i would try a 122 main,you are getting way to much gas if your runnin with choke on.move your needle setting and see if that does anything at all...

 

i put a 35 slow jet in and a 125 main in and it runs perfect, im goin to wait till it warms up to set the fuel mix screw i dont think that set right from messin with it from my past jets. thanks