I recently bought a 2009 KLX250SF and right away I noticed a problem. The bike tops out at 46mph!!! What the heck, everything is stock except for nice aftermarket rims, but would the extra weight of the rims really make that much of a difference?

Feel free to give me technical explanations I know enough about engines to understand what you are talking about.

 

Welcome to KF. Yes, that sounds like a problem.

Very unlikely its the rims. Is the speedometer reading close to accurate?

What gear and what rpm is it topping out? Can you rev up to somewhere around 8,000 to 9,000 rpm, and if so, through what gears?

 

I will experiment later today and get back to you. I don't have a problem getting up to 8000-9000 rpms but the horse power seems to drop significantly at about 7800-8000rpms. I will see the rpm's and gear it tops out in

 

Power does peak out around 8,000, so your observation is good. I was wondering if your motor was getting up to speed or if there was something (e.g. plugged air filter, poor jetting) that was preventing rev-up into the peak power territory.

Is your clutch slipping? Noticed by engine revving at higher speed but not putting power to the wheel. It would feel like pulling in the clutch lever somewhat.

How do you know everything is stock if you just bought the bike? What are your sprocket sizes?

Post up where you're located. Who knows, there may be a member nearby who'd stop by for a look.

 

Are the rims the same size as originals, 17”?

 

Just tried it out, (its about 25 degrees here so take that into consideration, as you can see it is snowing as well)

I topped out at 38 mph at 6500rpms in 3rd gear. Here is a youtube link to a gopro video of the dash when doing a full throttle acceleration


A couple things to note:

1) This was a full throttle acceleration test the whole time
2) When the mph starts going back down I was preparing for a turn at the end of the video
3) When I go from 2nd down to 1st the neutral light blinks as if I am passing through the neutral gear (it always does this)

Im in northeast Massachusetts

I will go check the measurements on the sprocket and rims

You're right, I'm not sure everything is stock, but the carb, jets, and exhaust all are and there is no big bore kit.

 

What's your gearing?? Maybe extremely over geared?? Will the engine bounce off the rev limiter(10.5k rpm) in neutral or with the clutch in?? Is your throttle opening all the way?? Did you buy it from a dealer?? If so take it back or try to contact the PO to see if he did anything to it. Is the carved jetted?? Easy way to tell if the carb was messed with is to check the a/f screw plug, if removed carb is probably jetted from the PO and something may be amiss there. How's the plug?? Replace it and test again.
Good luck

 

Stock gearing

It hits the rev limiter full throttle (barely)

Bought off craigslist but the previous owner (who I bought it from) is local and says he didn't do anything to it, but there was 1 owner before him but that's it.

The carb is jetted stock

I will try a new spark plug, but would that be that drastic of a loss in HP? The video is of the bike topping out, and it starts up first try every time (second try today because its really cold)

 

I also get about the same acceleration at half throttle and full throttle. Is that resulting from a loss in hp or is it messed up?

Tomorrow I will check to see if the throttle isn't opening all the way, even though it doesn't seem like that is the problem.

 

Pull the seat quickly, is the snorkle removed?? Or lid missing??