1996 xr400 wont Idle correctly

Hello all I'm new here but have gotten a lot of help from your forums before. Now I have a problem. I just rebuilt a 96 xr400 and now I can't get it to off idle correctly. I've cleaned the carb 4 times it's clean, I've checked for air leaks none to be found. When you throttle it, it either idles correct or it drops or it stays up. I have had a friend look at the carb also ( he is a motorcycle mech.) we found nothing wrong with the carb. I put it back on the bike and it still Idles good, bad, and back to dead. I'm at a loss. I have also checked the valve setting, all is good. HELPPPP

If you pulled the carby apart in the rebuild, check that you have the oring installed on the pilot screw.

Is this a bike you rode before the rebuild or is it new to you? Be sure you are working the choke lever correctly. Lever all the way up is full choke, all the way down is choke off. If you have this backwards, it would exibit the problems you're having.

Did you check/set the float level to spec?

If the pilot circuit is too lean, it can cause a surging and wandering idle.  Opening the fuel screw a half turn or two can solve this problem if all else is right.

I checked the o-ring is there and washer. I did ride the bike before the rebuild and it didn't do this. the carb was set aside during rebuild nothing was done to it till after the problem began. I did notice yesterday that when it sticks in the up idle I can tap the carb with a screwdriver and it will idle down. But what is going on I don't know I've had this thing apart and a mechanic had it apart and we can't find anything hanging up or wrong. this stupid thing is driving me crazy.

Baja rambler what do you mean by fuel screw? If your talking about air mixture screw I gone from all the way in to out.

We call it a fuel screw because it regulates fuel at idle in order to fine tune the pilot circuit.  It's at the front of the float bowl facing down.  When you open it, it allows more fuel to flow into the venturi richening the air/fuel mixture.  It has a spring, metal washer, and rubber o-ring.  Make sure the passage that feeds fuel to it is clear.  

  1. Ok Baja I thought that's what you were talking about. I've turned it in and out all over the place no change other than it spits when turned in to far or out to far. I have also noticed that when it is Idled up I can tap the carb and it will idle down but I can't find anything hanging up. I've tried to manually turn the throttle when Idled up and it wont change but if I tap it, it will drop.

Pull the carb and re-inspect the mixture screw o-ring. replace if questionable. Inspect the passage on the mixture circuit where this screw goes. verify that breather tubes are all clear and not crimped. if tapping makes a change in behavior, you have an intermittent mixture problem, all of which could be vent tubes, or mixture circuit.

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