aus rider 22 this one's for you

[1kx100]

I know that you have a 2000 yz125 like me and was wondering if the throttle response is good on it. Mine is terrible and bogs of the bottom. All the power is up on top. I have a procircuit pipe and shorty silencer. All the magazines say that this year is supposed to have a wide powerband but mine is extremely short. I rode my freind's 1999 kx125 and it had way better low end and the powerband was wider than mine, all it has is a rev pipe. Anyway, I was wondering if yours is the same, and if not what could be the problem with mine. Oh! and by the way this isn't just for aus rider 22, if anyone can help please do!

[Spitfire]

Sounds like your jetting is off, do a plug test and tell us what you find.

Another possibility is that your powervalves are stuck open, take your pipe off, and look up the exhaust port, you should see the valves closing about half of the port, if you don't see any valves, then they are stuck open, which would definatley cause horrible lowend.

[Aus_Rider_22]

Spitfire has put forward some good ideas to check.

I would say that your jetting it rich.
What jet sizes you got in her? If you don't know, the carb is pretty easy to take off.
What colour is your plug? I know alot of people say it's not really accurate on newer bikes, but just go WOT in as high gear as you can, chop the throttle, pull clutch in and roll. THen check plug reading. THis is will give good idea and probably reinforce our rich theory.

As spitfire said above, the powervalves are pretty easy to see by just removing the pipe.
My bike has same mods as yours (pipe, silencer) as well as carbon tech reeds. I can't really tell how the reeds helped as they were always on when I bought the bike. THe shorty silencer helped alot and gave bike harder hit. But yes, I would say my bike has good throttle response.

I can tell you a funny thing too. Even after these mods, I am still running stock jetting and fouling odd plug. I dove into the carb a while ago and found that pilot was way lean, and main was way rich. I reverted back to stock jet sizes and throttle crispness improved alot.

I recommend you do this and work from there. If anything you would think that after putting on aftermarket exhaust system, you would have to go richer, to compensate for extra flow from system. But I haven't found the need to change my jets from stock.

Hope this helps. PLease let me know if you have any other questions.
I run Motul 800 at 32:1 with 98 octane premium fuel.