KDX 200 acts like throttle slide is loose

[tgregg]

After 40 years of riding and racing I didn't think I could get stumped. I just got an old '86 KDX 200. It ran fine for 50 miles and then on the dirt road back to camp it started doing a weird thing. It wanted to rev up even though the throttle was constant. This is an air cooled bike and I suspected an air leak so I'm redoing the top end. My other thought was the float needle was stuck and dumping raw gas into the engine. As I took it apart I also found where it appeared the throttle cable might have been shorting to the spark plug wire which I know can cause some strange things sometimes.
I'm waiting on parts to get it all back together but just found this sight and thought I'd try it out.
So far in putting it back together I've replaced the float needle and seat, and put in Boysen reeds, and of course gaskets. Any thoughts out there?

 

[domino dave]

Sounds like you are already looking at all the things I would. Sorry I don't have any thoughts on your problem, but I do want to welcome you to this site. We have been pretty busy here discussing 2-stroke vs. 4-stroke, but hopefully someone will get back to you that has solved a similar problem. At any rate this reply will bump you back to the top of the posts. Dave

 

[tgregg]

Thanks, I'm an expert on 4 stroke vs 2 stroke!! Made Expert desert on a KDX 200 racing against open bikes. Retired for a few years went back out with a YZ 450 and hated that bike so much I didn't even own a dirt bike for the last 3 years! Thanks for the reply. I really think it was the float level, won't know though till my head gasket arrives. Mostly just wanted to get on the site!

 

[domino dave]

I had a bike one time that the float had a small leak and had some fuel in it ... Of course I thought everything was adjusted properly until I figured it out ... Drove me crazy. Dave

 

[dirt bike dave]

Could be a frayed throttle cable.

 

[tgregg]

Yes I thought of that but it doesn't "hang up" the revs just go up with the throttle held steady!

 

[tgregg]

I had a bike one time that the float had a small leak and had some fuel in it ... Of course I thought everything was adjusted properly until I figured it out ... Drove me crazy. Dave

If he needle and seat don't fix it new floats are next on my list. Your post on that was where I found this site I think. I Googled KDX and the problem and you came up.

 

[tgregg]

Got it back together enough to run it and it seems to run OK but gas is still pouring out of the over flow when the motor is off. New kneedle and seat so the next step is floats and plate. I'm going to play with the old plate and bend it until the gas stops over flowing and see where that is. May be a float issue. There is a reason they stopped using these dual independent floats. I maybe should just go looking for a later carb. Anybody know on the air cooled which carbs are better?

 

[tgregg]

I think I've solved the problem and fixed it. It would appear that the float needle and seat had a chunk of crud in it. Which allowed a lot of fuel to flow directly into the motor. This caused a couple of problems, one rapid reving of motor with throttle steady, second terrible fuel mileage! It felt OK when trail riding because I was at full throttle much of the time. It only became an issue riding down the powerline at steady speed. Then I ran out of gas at 30 miles out and 12 miles from camp.

 

[domino dave]

Thanks for keeping us up to date ... also good to hear you ride at full throttle most of the time !! Dave

 

[T_Bois]

It's great to get have closure. Thanks for post of what cure the problem.

 

[tgregg]

I also found the screen on the reserve intake in the tank was falling apart and had plugged the intake so very little fuel was flowing on reserve. I could get it to start after a few minutes and then the float bowl would run dry and it would die. Wait a few minutes and it would repeat.
Of course I'm running at high throttle setting when at race speeds it is only an old 200. My YZ450 on the other hand will go lots faster than I will!! I raced small bikes for many years and always thought you really don't need a throttle, just a kill switch :