Okay this is my first post here. Been lurking for awhile now. I recently bought a 2007 Raptor 350 from my brother in law. It had been sitting for about 4 years and only started once in that time I believe. I was going to rebuild the carb but I screwed it up trying to get the little main jet out. So I just bit the bullet and bought a new OEM mikuni carb. I finally got the chance to get it put back together and I can't get it to idle right. It backfires through the air box and then once its warm it just dies. Also turning the idle screw up or down has almost no effect on the idle. I did get it up and down the street a few times and it runs pretty good, it just won't idle. I have a brand new uni air filter on it, I also replaced the spark plug. I made sure both the inlet and outlet were sealed good and they appear to be. The only thing I haven't touched yet is the fuel screw, I thought that came set from the factory I am pretty new to small engines and would appreciate some help.

 

By idle screw, you mean the throttle stop? If so it has to affect the idle as it cuts the air/fuel supply to the motor. If the cable is too short, it won't allow the slide or butterfly to touch the throttle stop. An air leak in the manifold can also cause the idle to be all over the place. I have also had a faulty choke, of the type that lets extra fuel through, to be slightly open, allowing just enough through to produce a high idle with the throttle butterfly completely closed. Finally, if you got the carb from Yamaha, jets etc, will be pre-set for the Raptor, if you got it from somewhere else, they may not be.

 

Thanks for the reply. By idle screw I mean the idle adjustment screw on the carb. I looked at the carb boot and it looked ok. I should pull it off and inspect it better though. All the choke parts are new minus the cable. I'll have to pull the carb back off and drill that brass plug out to get to the fuel screw. Hopefully that just needs some adjusting.

 

If the slow running jet is sealed up, it should have been set right at the factory. Check that the throttle stop screw (idle adjuster) is touching whatever it is supposed to touch when idling. Also check the choke cable is long enough. Honda changed the choke plunger length in the carb on the 300 Fortrax mid production, same carb, same bike, two different lengths of choke cable required.

 

I'm not sure what you mean by the throttle stop screw touching whatever it is supposed to touch. The choke seems to operate fine. It does idle really high on full choke though. Not sure if that's normal.

 

The idle adjuster screw simply stops the throttle slide or butterfly from closing any further, it has exactly the same effect as shortening or lengthening the throttle cable. So the end of the screw should touch something when the throttle is released.

If the revs increase a lot on choke, it can indicate a weak mixture.