I have a '00 scrambler 400. what is ballpark on the high/low speed screws on my carb. i can get it to run fine up top but cant straighten it out on the bottom end. it will miss a few seconds and finally clean out. too, when i take off the seat, i can tune it to run fine up top but when i put the seat back on it runs like hell again. air filter seems to be fine. any suggestions?

 

The 400 doesn't have a high/ low speed screw, only the idle screw and air screw. The factory air screw should be at 1.5 turns out from seat. Make sure you don't have any clogged or pinched vent hoses.

 

bristolstud03
Have you done anything too your quad latley added anything? check for a pinched hose first , Running good up top usally means your main jet is good , I really do not understand the seat thing I really cannot see the seat blocking enough air to make a diff , try adjusting your needle

 

Raise the clip on the needle to the next notch and see if it improves.

 

I second ftwflh's opinion. The needle controlls your idle and low throttle position. If it is to low it is running rich.

 

Actually, the needle controls alot more of 1/4 to 1/2 throttle. Read here if you don't believe me. Or, run your needle rich one time and see where it affects the throttle range, I promise it will be in the 1/4 to 1/2. [img]i/expressions/face-icon-small-smile.gif[/img] The idle and low are controlled by the slide, air screw, and pilot jet.