Throttle sticking open on hills

[rocketman1]

My KDX 200 has a habit of the throttle sticking on steep up hill climbs, this happened in Taupo recently and almost caused me to crash.
I thought it may be dirt in the carburettor slide but it appears all clean except for the top of the slide where it appears the a little dirt has dropped into it from the inside of the throttle cable, I have now cleaned this out but dont know if it will fix it.
This will only happen, like once in every 3 hours riding?? beats me.
the cable is not pinched anywhere, the throttle snaps shut very quickly, so not binding the petrol tank is clean.
The throttle appears to stick at near full revs , which as can imagine, can give you a fright.
The jets are all clean as is the bowl.
Anyone had this happen, or can offer any good advice it would be appreciated

[FlangMasterJ]

Have you checked the throttle slide for damage?

[crazyxr250rider]

see if the needle is tight in the slide (or resonably firm)needle could be coming out of alignment and leaving the throttle jamed wide open

[FROSTY]

Take your twist grip assembily to bits.Dirt inside can jam things up OR there might be a bit of damage to the grip or the bar tip.
Do you have barkbusters? Maybee when the throttle is opened up to a certain point the tube is rubbing and jamming on the barkbuster

[crazyxr250rider]

He said the throttle snaps shut quickily so rules that out....

[pete376403]

If the carb snaps shut - is this with the engine running or stopped?
If the slide is worn, when there is no intake manifold vacuum the slide will move up and down fine, but when running under a high load condition (ie hill climbing, wide open throttle) it's possible vacuum is pulling the slide against the side of the carb bodyand it sticks. Are there any wear marks on either the slide or the sides of the hole? How old is the carb?
Somewhere I've seen references to air flow through the carb at WOT being enough to hold the slide up but can't find it.

[mattwood]

far, stuff that. would scare the shit out of me!!

good luck finding a solution though!

[F5 Dave]

PWK slides wear in these with a grin line when they are at idle, but this could cause an issue at higher openings esp as Pete says. The price of a new one will make you sit down but it does help Carburetion throughout. Erm mine 7 yrs ago was like $187. Maybe it was $87, but I think the former. But a full throttle crash could cost you more than that & you'd still have to fix it - if you were up to riding it again.

I would also remove the slide & try the throttle itself if slightly over extended does it hang up esp if there is sideways force on it?

[awayatc]

This may sound stupid, but with the cable being a bit to lose,I have had cable itself on full throttle go outside its guide on carb body and thus stay open, no matter what you do with throttle.... worth a quick check...( maybe combined with some pull on whole cable in certain conditions....
good luck:2thumbsup

[rocketman1]

Thanks for these items of advice guys, very interesting, I firstly thought it was grit getting sucked bythe air filter somehow and causing the slide to stick. But the filter is clean, so is the carby side of the filter intakes.
I have cleaned up the throttle control, and looks well greased and clean.
The slide looks in very good condition and only has some very fine slide marks on it. It does not appear to bind or stick anywhere, even after many times of twisting the throttle
The idea that the slide holds up under vacuum is interesting but the return spring although not strong should take care of that pressure, I would have thought.
Im wondering if dirt can get sucked down from the inside of the throttle cable at max vacuum and into the carb, ie.trying to get passed the slide but causing it to stick instead. I also thought the return spring was expanding when fully compressed into the slide and causing it to expand inside the slide and jamb it, but these are only ideas I have. everything else appears just fine.
The bike is a 1998 model, so the carb doesn't appear too worn

[F5 Dave]

The vacuum isn't that strong on a 2 stroke esp compared to a large bore 4 stroke. May be enough to hold the worn slide against an edge. But from the sounds yours is mighty fine so scratch that. The top doesn't have much vacuum either. However if water gets in it can cause issues.