Help PLz.

[Camaden]

Ok, I had a problem with my 300 ex idleing high, thought it was a carb problem, so I bought a 400 ex carb and put it on, when I first start it up and the machine is cold it seems fine but as soon as the bike starts to warm up it goes right back to idling high, so I know its not the carb now, maybe I should replace the throttle cable. I know your going to say I should have done this first, but I used this as an excuse to get another carb.

If after I replace the throttle cable and it still does this what would you guys suggest is my problem?

[dunny_mark]

Check to see if you have any air leaks from your exhaust or air boot. That will cause a high idle. Turn down the air screw on you carb.

[Blue250X]

dont 300's have a fuel screw, not air screw?? i could be wrong

[Camaden]

well it has a 400 carb on it, and now that you mention it I can see alittle bit of smoke coming out where the header bolts to the head, could that cause it ya think?

[Camaden]

anyone else?

[Sjorge450R]

Originally posted by Camaden
well it has a 400 carb on it, and now that you mention it I can see alittle bit of smoke coming out where the header bolts to the head, could that cause it ya think?

just answered your own question. Get a new gasket and then tighten them.

[Camaden]

this thing has a full fmf exhaust on it, I didnt see a gasket on the pipe where it bolts to the head is this normal? I did notice though that the flange might be bent alittle.

[GPracer2500]

There should be a gasket(s) where the pipe(s) connect to the head. They are metal crush-type gaskets that mold themselves into the head. They are quite hard to distinquish from the head itself once they get crushed into place. They are also a bear to remove once crushed. Flanges that bend inwards towards the head are a common occurance.

A leaking headpipe wouldn't generally cause a high idle though. [shrug??] Maybe if it was a really bad exhaust leak. Mostly it's an intake leak that will causes a high idle (caused by the lean condition created by the leak). Spray starter fluid all around the joints of the intake track and listen for a change in idle. If it changes (increases) at anypoint then you've found a leak.

Are you sure your idle screw (also known as the throttle stop screw) isn't just turned up too high?

[Camaden]

Yes, im sure about the idle screw, as soon as I turn the idle screw slightly to lower the high idle it imediately drops down to the point of the motor wanting to shut off.

Guess ill start by inspecting the air boot from the air box to the intake of the carb and the air boot from the carb to the head. Im also going to see if I can either replace the head pipe gasket and if I can find one, the flange on the header also.

Since I took off the stock 300 carb and put on a 400 carb, what air boot should I get so it fits properly, a 400ex one?

It also wouldnt hurt I supose to replace the throttle cabel itself.

Thanks for everyones advice in helping me with this problem, havent messed with this stuff since I owned 2 stroker 3 wheelers in the 80's.

[Sjorge450R]

Originally posted by Camaden
Yes, im sure about the idle screw, as soon as I turn the idle screw slightly to lower the high idle it imediately drops down to the point of the motor wanting to shut off.

Guess ill start by inspecting the air boot from the air box to the intake of the carb and the air boot from the carb to the head. Im also going to see if I can either replace the head pipe gasket and if I can find one, the flange on the header also.

Since I took off the stock 300 carb and put on a 400 carb, what air boot should I get so it fits properly, a 400ex one?

It also wouldnt hurt I supose to replace the throttle cabel itself.

Thanks for everyones advice in helping me with this problem, havent messed with this stuff since I owned 2 stroker 3 wheelers in the 80's.

I think that a 350x air boot works perfect.