On my brothers z250 when the choke is on it runs fine but when the choke is turned off all the way it just stalls.

 

is it warmed up good when you turn off the choke?

 

ya

 

idk, maybe the idle is to low.

 

Clean the pilot and or main jet in the carb.

 

im relativly new to carbs, how do i do this?

 

Try replacing the spark plug or any of the other many helpful suggestions in my thread: "Trouble with my Eiger"

 

Replaced the plug, didnt do anything. ill check that thread out.

 

you prolly just have to adjust the idle, get a screwdriver and turn the idle screw to the right (i think) to raise the idle speed.

 

It's definetely a mixture problem you are too lean right now. Heres what to do:
1.) Start it and warm it up.
2.) Turn choke off, does it stall ?
3.) Start it back up, with choke again if neccesary, take it for a ride. With throttle between 1/4 ans 1/2 turn choke off.

If it runs better than:
You're lean in your pilot circuit. Either you got crap in there or your fuel mixture screw needs to be turned out.

If it doesn't,then check like this in 1/4 throttle increments. If it runs better with choke on throughout throttle, you most likely have an air leak or your not getting enough fuel to carb. Try puttin the fuel valve in pri position. If it runs better than your vacume hose to fuel valve is either disconnected, blocked or your not pulling vacume from carb. Which would mean a blockage in the carb or an air leak between carb and motor. It could also be a bad fuel valve with those results.
You could also have a blocked float valve if you need choke, or just runs better with it, throughout the throttle range. If you find you're lean in some areas (Runs better with choke) keep this in mind. 0-1/4 throttle fuel mixture is controlled by fuel screw and pilot jet. 1/4-3/4 throttle fuel mixture is controlled by needle clip postion. 3/4 to wide open fuel mixture is controlled by main jet.