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I have an 05 klr250 and this bike runs just fine. My only problem is it is topping out at 43mph when i know that this same bike can hit 65 at LEAST. Anyone have any idea why its running so slow? My low gears 1-4 are just fine. It tops out at 43 in 4th, but i switch to 5th or 6th and go no faster. Help
 

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Just a quick guess with your limited info, you may have a pin-hole or a pinch in the large diaphragm on top of the throttle slide. If the diaphragm can not retain vacuum, the vacuum can not raise the slide to fully open position.

The twist grip is merely a request, intake vacuum does the rest!
 

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Good bet by pdwestman; SOMETHING prevents the lifting of your slide and needle.

Diaphragm leak (hole, tear, or IMPROPER SEALING ON INSTALLATION) might be the cause, or the slide may be somehow "jammed" so it cannot rise fully.

You might take a look at "Carb Overhaul," Page 3 of the "How To" forum, if I'm not mistaken, and go over your carburetor.

My own 2003 KLR250 can keep up with traffic on Interstate express lanes . . . considerably faster than 43 mph!
 

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Original poster here. Account deactivated for an unknown reason. I will be checking the slide sometime this weekend, as i am a fairly busy individual. Either way though, im certain the slide fully rises in that i can pull the throttle all the way back, and easily reach the rev limiter no problem. She is gonna be needing her valves checked and possibly adjusted sometime soon. Possibly its a transmission problem rather than a carburetor one in that i have taken apart and cleaned the carb recently. She starts within the first few kicks and runs just fine other than the flaw of topping out at such little speed. I've got a keihin 39mm carb laying out to the side which ran flawlessly on a 99 yz400f. Is it swappable with the carb i have now? Would that work? lol. Im always up to new ideas. My last resort would be taking her to a shop to see what the problems are, but i work a budget and like to get things done myself as it is much cheaper.
 

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The KLR250 don't have no stinkin' REV LIMITER, unless you consider the valves, intake and exhaust plumbing as such! :)

There is NO PHYSICAL CONNECTION between the throttle and the slide of the CVK34 carburetor on your KLR250; the slide is raised by "vacuum" (pressure differential) on the diaphragm. Pulling the throttle "all the way back" only opens the butterfly valve admitting air flow through the carburetor; the slide is raised, as mentioned, by the lower pressure in the venturi, piped above the diaphragm. Atmospheric pressure below the diaphragm actually raised the slide, technically speaking. An air-tight diaphragm seal is necessary for effective carb operation.

A 39 mm carb, likely, is wretchedly oversize for a stock KLR250 engine, in my opinion. A too-big carb reduces intake air velocity to the extent fuel cannot atomize properly, resulting in unsatisfactory combustion.

If I haven't done it before, I commend to you "Carb Overhaul" on page 3 of the, "How To . . . " thread on this website.

Also, while I'm commending stuff, I include, "Care and Feeding of the CVK40;" available from Googling or a "sticky" post on this website.
 

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Bryce,
With no load on an engine they will pretty easily rev til valve float or rev-limiter with about 1/3rd to 1/2 throttle. Which is all one gets with a pinch or pin hole in the slide diaphragm, inspite of the fact that the throttle plate is wide open. The slide itself is about 1/4 to 1/3rd open in the throttle bore. The throttle plate and 4 pilot outlet holes control the bottom 1/3 of carb opening. Above that the developed vacuum Must Raise the slide to allow increased air volume thru, but even a small vacuum leak in the diaphragm will preclude it from raising to full height. Major pinch or tear would preclude any lifting of the slide.

That same 1/3rd to 1/2 throttle is only good for about 4000-6000 rpm when engine is under load, in gear. So you get only about 45 mph worth of power to push you & the bike thru the air resistance.
 
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