All 2st Sticking throttle problem

Hello all,

Ive recently acquired what I think is a 1983 model WR250. The bike is a hodge podge, has the light kit and some other parts that are odd. The frame # comes back to a WR model but the plastic pieces say XC.

Anyways, The bike runs great except for one issue. Sometimes it seems like the throttle will stick wide open when the slide is actually not sticking. Here are the last two times it has happend to me.

First: I was in a sand pit goosing the throttle trying to kick up some sand. After about the 8th or so goose, it seemed like the throttle stuck and I found myself trying to fight it with the brakes. If I would pull the clutch in the engine would pretty much redline (at least sounded like it). It happened so fast I didnt try to hit the rear brakes, just the front handle brake. I ended up having to lay it over and make a quick get-off unfortunately, before I could kit the killswitch. Luckily I was in sand (this time).

Second occurance: Coming off a street (out in the country so no worries). Was in 5th/top gear, and gradually downshifting not letting the engine really engine-brake. When I got down in to first gear, it revved way up on me while I was turning off the highway. I pulled the clutch in and tried to get off but due to the holes and chunks missing out of the pavement and the sheer height of the bike I pretty much had to jump off since I couldnt really put a foot down.

It has a Mikuni carb on it. That is about all I can tell you. I took it apart and put it back together exactly as it came apart. It had some black slime on some of the floats and things like that. I cleaned every part in it and put it all back together and it fired right up and runs great but STILL behaves like this, infact the 2nd occurance I mentioned above was after I r&r'd the carb. The jets are clean and the needles are not worn or anything.

I appreciate anyone trying to help me. I will provide any additional info that I would possibly need to aid in assistance. Thanks!

I may go ahead and replace the throttle cable just to rule that out like you said. When I had the carb apart I soaked everything in carb parts cleaner before putting it back together. The round throttle slide looks immaculate and had no cuts or burrs on it, and neither did the center needle in it. When this odd behavior happens I try to keep pulsing the throttle grip to see if it is infact sticking and it SEEMS like its free because its returning but I cannot tell 100% for sure.

Being new to the terminology, Im not sure what a barkbuster is.

Well I took the bike out again today, and it did it to me twice. First, I was coasting in 2nd gear in the woods, I clutched, kicked down to first, and let the clutch out and the revs shoot way up. This time I stepped on the foot/rear brake and controlled it and the revs lowered after I fought it for about 1 to 1.5 seconds.

The second time, It started revving really high, I pulled the clutch in and stuck the bike in neutral and got off of it. Before I hit the kill I goosed the throttle a few times- It would rev up MORE but not come down. I shut the gas pitcock off and it was still going hardcore, however I only waited like 45 seconds (may have still had enough in the carb bowl).

Keep in mind, in all my occurrences of this I have been coasting or downshifting, except the first time I was in a sand pit in which I honestly do not remember what I was doing since it caught me way off guard.

Oh and rajobigguy, I do not have any barkbusters. The only thing I have around the brake and clutch levers are the original Magura leather pouch thingies...I dont know what to call them, but they have 2 metal snaps on them and they fit loosely.

When this happens can you feel the throttle tube stuck open? Or is the throttle tube/carb slide in the closed position while this is happening?

If the throttle is sticking open then swap the cable (make sure its routed correctly) and clean the throttle housing.

Ill make sure in the morning that its not going around any tight bends or anything like that. What keeps throwing me off (no pun intended lol) is that this problem happens MOSTLY when I havent even been on the throttle. Like I said, the other day, I was slowing down. 5th gear, clutch, 4th gear, clutch, 3rd gear, clutch, 2nd gear, clutch, FIRST GEAR and the engine revs way up (and no i wasnt really engine braking, I was easing on the front brakes at the same time as downshifting) and when I try to fight it with the front brakes it starts doing a burnout with the back end.

A friend of mine told me to check my high rpm needle. Everything checked out A-OK when I remanned the carb the other night. My thinking would be if the high RPM was clogged it wouldnt run right to begin with. If it wasnt shutting off or whatever and just letting gas keep on going wouldnt it just totally flood out due to the throttle being closed. A ton of gas + no air = pig rich condition.

Two More Things to Check

OK, so if you've cleaned the throttle barrel, lubed and checked cable routing, looked at the condition of the slide and needle, you may want to consider these two things ...

a) if you have old gas in the tank, it could be causing the "panic rev". Whatever it is that evaporates takes away the stability of the fuel (I had a KTM125 that threatened to grenade itself until I emptied all of the old gas and freshened up)

b) you may have an air leak, either by a crank seal or in the intake tract. Spraying a mist of WD-40 or ether near the intake (between the carb and the cylinder) and causing a increase in RPM would indicate a problem here; removing the ignition cover and doing the same with a resultant rise in rpm would indicate a bad crank seal; the other side is harder to diagnose

Thanks twowheels! I will definitely try that! I dont think its old gas in the tank since I have used about 8 to 10 gallons through the bike via riding and what not. Your "B" point may be what my problem is. Occasionally while idling, if Its breezy outside, I can see blue exhaust smoke (a tiny bit of it) coming from the engine area. Ill check and see if the intake and reed assembly is all cranked down good and Ill check the exhaust assembly. Ill check it out and let yall know! I appreciate it!