1999 YZ250 No power High RPMS

[Cleric]

Backround Info: Did a race in sept and towards the end of the race the bike lost all top end power. SO i just finished up redoing my topend, new piston rings everything.


Got the whole bike back together and now in high rpms about 3/4 throttle the bike runs terrible, feels like the choke is on.

Does fine in the lower RPMs and starting just once i get on it it wont hit the powerband it just bogs and has no power. Basically no top end pull.

Before putting the bike back together i cleaned out the entire carb, airfilter, and it has a new plug. Has the same jetting that ran perfect before.

Is it electrical or possibly powervalve?

Any help would be greatly appreciated.

Thanks

Cleric

 

[IZ 250]

Sounds to me like your powervalve isnt working properly. Did u hook all the parts back up to the powervalve?

 

[Cleric]

im almost positive i did, is there a way to test or check if my powervalve is working properly?

 

[jabbahoo]

i would also like to know this. My dirtbike is doing the same thing

 

[phranticness]

take a look at the reeds. I had a simular problem, here is a link to my thread

http://www.dirtrider.net/forums3/showthread.php?t=138699&highlight=kx250+bogs

 

[Cleric]

checked reeds and powervalve and still having trouble.


Any other suggestions?

Any electrical tests i could try?

 

[jabbahoo]

Would a spark plug cause this? Mine was doing the samething. So I put in another plug and walla.

 

[Cleric]

no ive tried a new plug still nothing

 

[loudandproud]

sounds powervavlish like problem.


You like my new word, admit it.

 

[Cleric]

i took the cover off the powervalve linkage and ran the bike and it seems to be moving up and down.

Could there still be a problem internally?

What would be the best way to go about cleaning it?

 

[jabbahoo]

What do you take off to check the powervalve?

 

[Rootuser]

Power Valves

There are power valve covers to remove and you should probably remove the pipe to get at everything. They are like a little extra section on your cylinder head that isn't quite part of the cylinder.... kind of hard to describe....


As for reeds, if you had a broken reed the bike would not idle at all I believe so I doubt it's a broken reed.

You mention 3/4 throttle.... Is your pin setting correct? Beyond 3/4 throttle however does not effect anything as you are wide open and it's all up to the main jet at that point.

I am having a VERY similar problem myself and I am working on diagnosing it tonight I think. In the mean time check out this thread:

http://www.dirtrider.net/forums3/showthread.php?t=141770

It may shed some light on possible things to look at.

-- Rootuser

 

[1989kx250]

is the choke on? just throwing it out there.

 

[ryan callies]

The rod may move and the valve still might not be opening. Pull the pipe off and see if the valve moves with the linkage. You could have a screw missing or some thing broke. Good luck, Ryan -Finish Line Engines