engine cutting out, need help!

[lilpoppy]

Here is the deal. My friend and I just got our 400ex's back and we started breaking them in today. We both have x-6 exhaust, 416 kits, hotcams stage 2, and porting but now his is having trouble idling and it seems to be running fine but when you come to a sudden stop from riding it just dies every time. I don't know much about the stock carb because I got a FCR almost right away so we need some help. What do the 2 screws on the carb do? We tried adjusting both of them all the way in and out and neather seem to change how it runs at all. I mean it seems like those screws make absolutly no difference whatsoever when we turn them. He is jetted at 170 dyno jet, and a 42 keihin jet with the clip on the needle one notch below stock. Please help us out we have a big trip coming up in two weeks and we need to get this fixed.

mine does that when it overheats after a long ride

[toby400ex]

Maybe you should adjust the idle :huh . Does it idle right when it is just warmed up. The Air screw will just mess with the back firing and what not, i dont know of any other screw, excest the springy big screw that you turn to adjust the idle.

[lilpoppy]

No I don't think it idles better when it is warmed up. The only way we could get it to idle was by tightening the throttle cabble up until it was holding the idle high enough. As far as I know the idle adjustment is the big screw that is under the carb on a bracket and it is sticking out sideways right? We tried messing with that and it does nothing at all. It doesn't even adjust the idle the slightest bit. Is it possible something disconnected inside the carb which is causing it not to work properly?

[KY Woods Rider]

You said that it ran fine, but I still have a question about how it runs. Once it gets warmed up to normal operating temp, does it have a bad hesitation/miss when going from low RPM (just above idle) out of a tight corner up to maybe 1/2 throttle as it's pulling out of the corner? The reason I ask is because you say it won't idle and the screws don't do anything. To me that sounds like an air leak somewhere, most likely a blown head gasket. Check around the the head gasket and see if you see any oil coming out.

[lilpoppy]

It is kinda tough to say because he was just breaking it in so he wasn't getting on it very much at all. I will have him check out the gasket but I don't think it is blown. I rode it once and it didn't seem to have any hesitation at all. It seemed to be running perfect it just dies when you come to a stop.