Guys, have a 2006 Sportsman 500 HO Carbed unit, has 2600 miles, unit starts fine, but will not idle when cold. If I leave the choke out part way it helps, but the engine runs like it is over-fueling. Prior to this problem, I seldom had to use the choke upon cold starting, and it Idled fine. I have removed and cleaned the carb, checked float level, removed plug from air/fuel screw adjuster, no matter the screw position, engine seems to run the same. This got me thinking I may have a plugged or restricted Idle circuit, so I removed the carb, completely disassembled, soaked, and blew out all passages with compressed air, reassembled. Still the same situation. Quad runs great, and Idles fine when warm. If I move the idle screw/cable so it will idle cold, when it warms up, it will idle over 2000 rpm. I'm at a loss

 

Did you replace the needle and seat in the carb or just cleaned it? Plus check for any cracks/air leaks in the carb intake manifold. How many turns out on the idle screw mixture? Plus did you save the small washer and o-ring on the idle adjuster(fuel air screw) ?

 

Thanks for the reply OPT, no I did not replace needle and seat, cleaned and inspected, it looked ok. Have not checked the Carb intake, guessing your talking between the carb, and engine? I'm currently 2 turns out on the screw, and yes the Washer and oring are on the adjuster for air/fuel.

 

If you still can't tell any difference when you adjust the fuel/air screw then something is still up with the carb! I'd replace the needle and seat and check out how the float level is supposed to be set. Here's basically the same BST40 carb,but is used on a KTM,so a little different on the out side. The BST-40 Bible - ADVrider

 

Well, as you recommended, I replaced needle and seat, adjusted float, and air fuel screw at 2.5 turns out, and the quad now starts right up, and idles fine, just like when it was new. Thanks OPT!!

 

Glad you found the problem and posted for the other fellas that may experience the same problem.

 

This sounds like the same problem I'm having.....

 

That's why I'm glad people post back on their solutions to problems! Their posts may help people like you!

 

Right on OPT! Every little bit helps...