This was done 3 years ago. I just had jug reworked. I did all assembly..
-Ported jug
-Wiseco piston
-38mm carb (15 primary, 340 main jet, e-clip center position on needle)
-HSP pipe
-V-Force reed
-Clutch kit
-K&N filter

I just rebuilt w/new piston & cylinder rework, but this was same problem I had w/previous build. I have owned since new. It will idle ok when first started w/choke, but it then will die after about 3-5 minute. At that point any amount of turning in idle adj screw won't correct. The only thing that works is to adj throttle cable to give carb some pre load (raising of slide). At that point it is perfect, but I know that is not right. It had a 20 pri jet in it, I thought maybe I was flooding it so I went down. I could go to the 25 that I have, but I'm not sure.
Note: This Scram hauls *** now all the way through rpm range. It will wheelie like all hell from a slow speed. I just would like to get idle corrected, winters coming.

Thank You...

 

Pull the air box off, look in the back of the carb, screw in the idle screw. Does the throttle slide raise? If so, take carb cleaner and spray around the intake and the cylinder gasket and see if the idle changes? Does it?

 

Thanx for the reply.
By the way, it is a 2-stroke (forgot that part)
I have air box off while trying to adj slide. I have gone as far as to turn it in so far that it will actually deadheads against side of slide causing it to bind. I start with adj screw competely dis-engaged from 'ramp' slide all the way down. As I turn it in, it raises slide nicely, but it still won't stay idling (unless of coarse I pre-load w/cable adjustment near throttle lever). I had carb totally apart several times in last week, I cleaned it as well I could w/carb cleaner. I am mech inclined, but not a carb expert by any stretch.
I wonder if there is an air leak somewhere? Could read valve condition have an effect?

 

is it possible to put the slide in backwards in this machine? (the higher part of slide face needs to be on the airbox side)

 

have you pulled the pilot jet out and made sure it was clean?

 

like most 2 stroke carbs it should be almost impossiable to put the slide in backwards. i dont see how you bind the slide w/ the idle adjustmne tsince their both on a tapper. when you turn in the screw it should lift up the slide. make sure the idle circuit is clear and free from dirt.

 

Morning,
The slide is impossible to put in backwards. It is a flat slide w/a bump out toward the front.
The idle adj screw, if it is turned in to the max, will bottom out beyound lifting ramp and 'dig' into side of the 'bump out' part of slide. (Bind will occur)
Jets are brand new and clear.
Today I will try puting the 25 primary jet. I started w/the 20, then went to the 15. I will now try going up. The carb is relly clean.
OH, I will also try spraying carb cleaner into carb and report what happened as 94harley recommended...

Thanks again for all the replies...

 

While the carb is apart inspect the idle screw and the tapper on the slide where the screw rides.The slide and screw can wear causing this problem.

 

I'll bet the carb is a TMX. I beat my head against the wall trying to tune one of those. I finally went back to a 34mm round slide. The idle screw design on those is terrible. I talked with Mr. Aaen about it and he said to use the throttle cable, as far as the pilot, rule of thumb is to use half the size of what you had in the round slide. Make sure the cutaway on the slide is spec'd right and also the needle jet is right. Doc

 

Yes the TMX is a bad match for the 400 but it can be made to work if you have the patience. Drop to the 10 pilot, open the airscrew 3 turns and see if that helps. The lack of needles to tune the carb is the biggest problem, to rich at idle and to lean from mid to wot. I retapered my own needles to get the correct mixture, PIA!!!!!. I also built up the idle ramp on the slide with epoxy to cure the idle problem you also have.....