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CR250 throttle runaway

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Hi, having some trouble with my 1996 cr250. Purchased the bike and at the time it wouldn't idle, hard to start and the bike felt rich wide open. Worst part is the throttle stuck a few times.

 

Figured it was the worn parts in the carb. Replaced al parts, throttle cable, fresh piston. Fiddled with the jets and bowl hight, still didn't run right.

 

Bought a used air striker, best mod ever.

Now it runs phenomenal, idles and starts 1 kick. All my problems disappeared.... I thought.

 

The throttle still runs away, the strange thing is. Only every 5th ride. It's not wide open, and the build-up is slow till half throttle.

 

Changed the reeds, checked the routing of the cable, new exhaust packing, even put sealer on air booth part to the cilinder and seams of the bottom half of cases.

Sprayed brake cleaner behind the stator, bike did nothing strange.

 

 

I'm lost. Could it be caused by a rich or lean setting and slow trails, which overflows the bottom-end and ignites?

 

 

 

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If everything mechanical has been ruled out (frayed cable, throttle tube binding, damaged slide, hang ups in the carb etc.)

look into doing a crank case leakdown test, there is a sticky on top of this Honda 2-stroke sub-forum.

 

25$ worth of simple auto and hardware store supplies builds you a handy test fixture, 

a valuable tool anyone who wrenches on a 2-stroke dirt bike should have to troubleshoot with.

30 minutes of your time can save you hours of headaches by ruling out air leaks or bad crank seals.

 

Just a note on sealing the reeds / air inlet,

regular automotive RTV or 'silicone' sealers are not the right product for the job,

any contact will gasoline either in liquid or vapor form will eventually turn it to mush.

 

Gasoline resistant sealers like Yamabond, ThreeBond or Permatex Motoseal is what you want,

every bike manufacturer has their version it will be marketed as 'gasoline resistant engine case sealer'.

 

Edited by mlatour

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If everything mechanical has been ruled out (frayed cable, throttle tube binding, damaged slide, hang ups in the carb etc.)
look into doing a crank case leakdown test, there is a sticky on top of this Honda 2-stroke sub-forum.
 
25$ worth of simple auto and hardware store supplies builds you a handy test fixture, 
a valuable tool anyone who wrenches on a 2-stroke dirt bike should have to troubleshoot with.
30 minutes of your time can save you hours of headaches by ruling out air leaks or bad crank seals.
 
Just a note on sealing the reeds / air inlet,
regular automotive RTV or 'silicone' sealers are not the right product for the job,
any contact will gasoline either in liquid or vapor form will eventually turn it to mush.
 
Gasoline resistant sealers like Yamabond, ThreeBond or Permatex Motoseal is what you want,
every bike manufacturer has their version it will be marketed as 'gasoline resistant engine case sealer'.
 
Ok, thanks. Leakdown test seems a good idea. I will start with that.

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13 hours ago, koningwim said:

 

Hi, having some trouble with my 1996 cr250. Purchased the bike and at the time it wouldn't idle, hard to start and the bike felt rich wide open. Worst part is the throttle stuck a few times.

 

Figured it was the worn parts in the carb. Replaced al parts, throttle cable, fresh piston. Fiddled with the jets and bowl hight, still didn't run right.

 

Bought a used air striker, best mod ever.

Now it runs phenomenal, idles and starts 1 kick. All my problems disappeared.... I thought.

 

The throttle still runs away, the strange thing is. Only every 5th ride. It's not wide open, and the build-up is slow till half throttle.

 

Changed the reeds, checked the routing of the cable, new exhaust packing, even put sealer on air booth part to the cilinder and seams of the bottom half of cases.

Sprayed brake cleaner behind the stator, bike did nothing strange.

 

 

I'm lost. Could it be caused by a rich or lean setting and slow trails, which overflows the bottom-end and ignites?

 

 

 

 

If your getting a run away surge in throttle while holding it at half throttle that means your lean.  Half throttle is your needle

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