Hello fellow riders!

I have a 1996 Sportman 400 2 stroke that refuses to idle unless the choke is on.
With the choke off I can hold my hand at the mouth of the carb and regulate the idle manually. When I remove my hand, or have the filter in place, or leave it alone it will run for about 5 seconds then die out.
The carb has been rebuilt and pulled apart twice to check for obstructions and proper float level. Carb Cleaner and air blown through it! The float arm is set at parallel to the gasket surface just as the manual says it should. And if the floats were bad it would flood because they would sink, and the needle would open,
I've tried different needle positions on the throttle slide to make sure the main jet isn't supplying the idle. The pilot jet should supply the idle. The cable safety swith wouldn't come into play because it run with the choke open.
The idle screw is turned out 4 turns now and it's still a no go. Originally factory is set at about 2.
The idle speed screw that holds the slide open for idle set really doesn't do anything due to some dimples on the slide where it has contacted on the ramp. But even manually at idle speed it still dies out.
I've sprayed and checked for vaccuum leaks to no result. When I hold my hand to the carb mouth it's like holding it to a Hoover.
The engine has all of 5 miles on it and it ran and idled last summer, albeit not as smooth as I would like.
It's like the idle circuit isn't working.

Any suggestions or ideas? I'm stumped and a fairly decent mechanic. Would bad or old gas do this??
Sorry for the long post, just trying to be thorough.

 

yes bad gas can cause crappy running. the carb is designed and jetted to have the air filter and box cover on to richen it back up. it does sound like the idle circuit it is plugged( and i know you mentiond in the other post you did about cleaning it)preventing it form idling. you mentioned the idle screw isn't working?? if it is put together correctly on the slide the screw turning in should be lifting the slide up as you screw it in to idle it up. you set the throttle cable first then adjust your idle setting. what do you have the air screw set at?

 

There is an air screw? I didn't see one. The two screws are the pilot mixture screw and the idle screw that controls the slide. The idle screw is set all the way in. No difference. The pilot screw is out 4 turns to get it richened up enough. It's almost loose!

I'm chaning the gas with new tomorrow. Drained tonight. It's still in the carb, though.

Do you think that the slide is still open too far to send the vacuum signal to the pilot/primary side of the carb? I haven't messed with the throttle cable because there is slack at the thumb lever, which tells me that the slide is all the way down in the carb bore.

 

You are probally running too lean at idle.The air mixture screw is supposed to be turned in to richen and out to lean. I thought it was opposite until I read it in the repair manual. It should be set at 1.5 turns out after seating.

 

Holy moly...I didn't know the screw was opposite. I hope that's all it is!

The air mixture screw is the small one closest to the carb inlet, isn't it?

 

the air screw is NOT THE pilot jet. the jet is a fixed jet just like the main jet is. if you didn't remove the pilot jet for cleaning that could be part of the issue. like mentioned the air screw should be about 1.5 turns +-. your idle is way too high.w/ the screw all the way out you should adjust the cable so that the slide is botomed out in the carb and then use your idle to bump it up. hopefully that clears it up a little for ya. good luck

 

Clean the carb once more. Here is instuction on how for your slide carb. Disassembly and Cleaning of a Mikuni Round slide Carburetor