Sudden Full Throttle

[TomDez]

Has anyone experienced the following on their KDX 220:

After landing a jump, the bike suddenly goes to full throttle without any throttle input from the rider? This has happened to me twice on my KDX 220, both times on a hardpacked motocross track. It has never happened in the woods.

One of my riding partners used to have a KDX 220, and said he had experienced the exact same thing on hardpack tracks.

Does anyone know what causes this? Can this be fixed? I have checked the throttle cable, and cannot find anywhere that it may be hanging up upon decompression of the suspension after landing the jump.

I love my KDX, but there is no way I can continue to ride it in the woods knowing that it is prone to this.

Tom

 

[5810]

Check cable routing.
Check the cable & lube it. also check the twist throttle & lube it, & check the carb slide!!!! Make sure its clean. (mine was packed with grit when i bought the bike).

Good Luck. & let us know what you find !!!!!!!!!

 

[Hoffies]

For how long does the sudden full throttle last, or does it stay wide open??

 

[julien_d]

Definitely not a normal characteristic of KDX. Something is wrong. Most likely it's in the cable/slide assy as 5810 said, but could also be a fuel delivery issue.

J.

 

[mudpack]

For how long does the sudden full throttle last, or does it stay wide open??

This was the first question that came to my mind, as well.
We need to know the answer before an intelligent reply can be made.
If it hangs wide open, how do you correct it? That will tell you what is causing it.
If it is just a momentary burst of WOT, then the cause will be different.

Give us more information. :nod:

 

[Kx85Krazy]

why are you riding a KDX220 on a motocross track anyway?

 

[2strokesrock]

could the G-forces or lack of cause the bike to lean out momentarly? just grabbing at staws :)

 

[rompnstomp]

Maybe a weak return spring on the carb slide/throttle cable. Think to yourself "why doesn't this happen to every motocross bike out there" and that should answer your "lean out" question. All things being equal, look for the mechanical and ignore the mystical. I could see the rebound "bounce" upon landing causing the slide to go up a little if your return spring is very weak and your throttle cable has lots of slop in it.

 

[mudpack]

We need some feedback, Tom.

 

[TomDez]

The bike hangs at what seems to be WOT. The first time it happened, I pulled in the clutch and it continued to wind out until I hit the stop button. The last time, no such luck. Grabbed a handful of front brake and went down, the bike died on its side. Both times it started normally afterwards.

 

[_JOE_]

One way or another there is too much air getting in. Check the carb boots very closely for cracking and pull the carb apart an inspect it under a bright light.

 

[mudpack]

So, it is STAYING at WOT when you give it full throttle, rather than GOING to WOT on its own?
Check your throtle cables and the carb slide.
Is your air filter in good shape? Grit getting into the carb could be causing the slide to hang up momentarily; you should have no air leaks between filter and intake port.

 

[rompnstomp]

I agree with mudpack...make sure the throttle cable isn't backing out of the top of the carb slide cover also...had that happen before and that will cause it to hang up...usually a cable routing problem in that instance.

 

[dirt bike dave]

FWIW, the only time a KDX stuck a throttle on me, a close inspection showed the throttle cable was frayed near the carb. If the cable is frayed somwhere inside the sheath, you might never be able to see where the problem is.

A fraying cable can cause intermittent sticking, and a lube is not going to cure it.

On mine, I replaced the cable and fixed the problem. I think a new throttle cable was less than $20 at the time.

I really think you should replace the throttle cable before your next ride. Make sure you route the replacement cable correctly.

 

[rompnstomp]

I bet a new throttle cable is still less than $20. :laugh:

 

[duson]

I had this happen to me and went flying into the woods as a result :(

When I recently had my bike worked on, the guy said that it was missing a circlip on the bottom of my throttle cable that was causing the spring to catch every now and then - the part number is 92036-018. I just ordered one, and will let you know if it fixes mine.

 

[Teamgreenfan]

I had the same thing happen to an 89 KX250. My friend would jump and land and hit full throttle almost every time. A very long story short, we finally found that the needle was sticky on the float causing the bowl to have just enough in it to run fine on the trails, but the fuel would slosh in the bowl it would starve it for gas and idle up a bunch after a jump. We were able to duplicate this by shutting the fuel valve almost all the way and letting it idle and slowly shutting the fuel off. I would suggest just cleaning the carb and resetting the float and I'll bet that will solve the problem.