Sticking Throttle

[jeffw]

Duneman,
I don't agree. With a closed throttle slide there's no way for air to flow through the carb and suck more fuel through the main jet. I guess a crankcase air leak *could* cause a blip in RPMs but fuel in the the crankcase would be quickly burned and the bike would return to idle RPMs.

My condidtion was sustained WFO with a slack throttle feeling. I pulled my carb again this weekend and closely examined the needle and found two nick marks. The only thing that I can imagine could have caused these were very small pebbles stuck between the needle and main jet circuit, thus holding the slide open.

 

[Duneman]

if you are riding at half throttle and instantly it starts to rev and you shut down the bike it will still go wfo long enough for you to wipeout. That's what I am talking about a crank leak, I checked my carb slide and mine had little nics as well but I checked everything cable, throttle spring, slide spring, slide, and it would still do it. I could ride all day and it would do it only once then the next day 3 times, day after that not at all, if it happens at random like that then most likeley it's an airleak. hope I'm wrong cause if it's a crank leak the cases half to be split.

 

[DCMan]

This happened to me once this year. I was fine luckily. Mine definately was not an air leak. I had the above mentioned slack in the throttle. No spring tension whatsoever! There could possibly be more than one cause for this. It hasn't happened in a couple of months now, and I never found any kninks or blockages.

 

[70 marlin]

maintenance, maintenance & more maintenance! remove and clean twist throttle, inspect & lube cables. check out routing of cables & hosing. pull, clean & inspect carb offen! replace worn parts! if you show the love and do it correctly every time you'll rarely see throttle problems.

 

[craig_enid]

My $.02.... had the sticking problems after removing and re-installing carb, tank, bars, etc. For me, the problem only happens on whoops while WFO. The angle I'm working is the throttle cable being routed wrong, and getting into a bind during the up and down movement of the cable. Sounds like a correctly routed cable may have the same problems, if my theory is correct.... and judging from the number of responsed.....
Also, mine pulls WAY too hard during those events to be a lean condition. The main jet is definately in play.....

 

[jeffw]

Also, mine pulls WAY too hard during those events to be a lean condition. The main jet is definately in play.....

Yeap, same kind of power surge experience I had. There was no way my experience was an air leak of some kind causing high idle. The throttle slide was definitely open somehow and the main jet was delivering fuel, just how far I can't say for sure, but it sure felt like WFO.

The whoops theory is interesting and others have mentioned it also. Could the fork action have caused your throttle cable to catch on top your brake hose and lift it thus stretching the throttle cable for an instant?

I'm still convinced mine was caused by a stuck needle in the main jet circuit since my bike stayed wide open until I got it stopped with the kill switch and subsequent carb inspection showed lots of dirt in the bowl.

I'm sure there's more than cause out there.

Edit, whoops I meant: I'm sure there's more than one cause out there.

 

[craig_enid]

My thinking is the cable 'bouncing' around to a point where it's lodged and pinched. It only happenes to me during whoop sections, and the throttle Stays open, it doesn't open on it's own....

It's amazing how much stuff we do by instinct or reaction without thinking, when we ride. When the realization hits that the throttle is stuck, my brain functions slow to a crawl and I have to think about where the brake pedal is, how much to push on it, where the clutch lever is, etc.
I'm tied in now so when it happens, I just lock up the rear brake. Then, if conditions warrant, I'll twist the throttle once or twice to see if it frees it up. I can usually get it released before coming to a stop.
Jeffw, you said the needle sticks, but in my mind the slide is more likely the culprit...

 

[jeffw]

Craig,

I'm talking about the slide needle. Since its attached to the slide if it gets pinched in the main jet circuit by a tiny pebble the slide stays open too.

Close inspection of my needle shows two distinct nicks. I have no idea how these got there other than by what I've described.

It happended to me accelerating through a field in the middle of a gear shift. When I blipped the throttle slightly from WFO to shift gears it stuck open. Kind of makes sense when you think about it: High flow of dirty fuel from a dirty float bowl + tapered needle falling into the circuit = :scream:

 

[craig_enid]

Jeff, yes, your described scenario would be the needle sticking....
Do you run an inline fuel filter?

 

[Kawierider]

Hey guys,
on past bikes i have had the problem with a sticking thottle usually it ends up being dirt or the cable. however, with my dads kdx i had the problem and i found a very strange cause.
while riding down a trail i dumped the bike in some deep sand. i picked it up started it with the choke....cause thats all that would work and rode it back to my camp....wit hthe choke on. To make a long story short for intermittant periods of time the bike would run fine with no choke except for the throttle would stick open occasionally......luckily it resulted in only missing turns thanks to a quick cluthc hand.
I tore the carb aapart and found that i had somehow broken the needle off clean at the clip and it was sitting in the seat. the only throttle control i was getting was from air and the excess gas given from the choke circuit. the thrrottle stuck probabley because the need bounced up and jammed the slide.
now when i rejet or rebuild the carb i always check the slide for wear, and cracks using a magnifying glass. it was probabley a fluke but jeff freddette didnt make frp from letting "flukes" slide by. good luck, hope it helps
Tim
ps it was an 88 200

 

[NZMXr]

I had the same thing happen to me when my bike was 2 weeks old , as I came up to a corner ,the throttle stuck and as soon as I hit the front brake over I went

 

[Bryan Kimsey]

My throttle stuck just a few weeks ago and what I found was that the brass tube exiting the top of the carb was bent just a little bit and grabbing the cable. When I tried to straighten it, the tube broke, leading me to think it had been like that for a bit. Fortunately, just the threads broke and I still have enough to re-thread so that's what I did.

Also, check the throttle tube on the handlebar- I've had that problem before.

 

[KDX'r in IN]

Happened to me just last weekend. Everything was sealed up good and I could not see anything wrong with carb, cable, etc...By the way happened 2nd gear downhill, my buddy just said "what was that". No damage to me or it