Hey, just joined the forum but I have been enjoying my 2009 klx 250s since September 2008. I have slowly been doing all the necessary mods. over The past 2 years and now I am playing with the idea of going to a 13 tooth front sprocket. I am currently running a 14 front (stock) and a 45 back which was the first mod that I did early in the spring of 2009. It helped the low end and I only gained about 500 rpms at 90 km/hr. 90 is about as fast as I need this bike to go on the black top because most of my riding is trail riding (four wheeler/snowmoblie trail and dirt roads. Any comments on dropping 1 tooth up front, will it rev through the roof on the pavement?

P.S. Mods that I have already completed:
- FMF Q4 slip-on
- Removed air box lid
- installed a UNI filter
- took the bike to local engine guy and got it rejetted on the Dyno
- moved up 3 teeth on the rear sprocket
- Moose skid plate
- Acerbis hand guards
- Mt 21 front and rear tires
- 1.5 inch bar rise kit
- cut off rear fender extension (to tidy up the rear end)

I have one more question, after all the mods ,this bike topped out on the dyno at @ 23.85 horsepower. Is this about what everybody else is getting or am I way of the mark?

Thanks

 

welcome MTB. I am also looking into changing my C/S sprocket this winter, and experiment a bit with regearing.

I think Deej has the 13/45 gearing so I'm sure he could tell you what his RPMs are at various speeds. Just remember, changing one tooth on the front is the same as doing 3 in the rear (42/14) stock ratio, so with that quick thought I would think your RPMs would double from the original rear sprocket swap to an additional 500 RPMs at 90 km/hr.

I haven't taken mine to the dyno but I have similar mods to what you've listed so I would expect mine to be similar.

My Gravely riding lawnmower has a kawasaki 25HP engine in it, and my bike feels slightly more powerful than that

 

By dropping 1 tooth on the front you'll experience the same change again. 1 frt = 3 back. It will be revving pretty high on the highway. You'll have increased the revs 14% total (7% each time)
ps: psudude posted quicker

 

I'm running 14/49, which is very close to 13/45 (just slightly shorter). The bike definitely is revving high at about 55-60mph, i wouldn't want to hold it sustained at that speed for more than a few minutes. Otherwise it feels great, you will spend very little time in first gear under normal riding conditions, and can just reserve it for a sort of 'low range'. The bike pulls better also. If trails are your focus, I'd go for it.

 

As far as power goes you started at about 18-19 Hp and you are now at 23-24 so that is pretty good for the mods you have.

 

Check out the gearing commander website. It's fun to play with and will help answer your questions. http://www.gearingcommander.com/

I'm running 14/49 right now. I don't mind riding 60 to 65 with it for a while, but 75 is too much for my comfort. Also have a 13 and 15 front sprocket. I haven't tried them on yet as she's in major winter teardown and maintenance mode right now, but expect to use the 13 here and there when I do the slow and technical trails, and the 15 for running around the desert.

Someone commented that I may have a tough time removing the chain, and thus tire, with a 14/49 without first removing (or at least swinging) the chain guide. It's a little tight, but is definitely doable. The 13 will be easier. The 15 may require swinging the chain guide. Kind of like changing the belt on a VW...

http://www.youtube.com/watch?v=BQhfcdQf1QA

 

Quite the belt change. Thanks for showing that. 1967; the best year of VWs!!

 

Now do that with the chain on a running '06 KLX and you'll be Mr. Cool .

 

Pretty cool belt change. I had a '64 Beetle. If it only could talk...,

The only thing you can do is try the gearing and see what works best for you.

I think the 23 hp is a lot, what jets did you end up with?

David

 

I got out my Dyno analyzer and I was wrong at 23.85 horspower, it was actual 22.55, stock 16.64. It looks like it maxed out somewhere between @ 8000 and 8500 rpms, after that it pretty much flat lined. Here are the technician's notes, they mean nothing to me, air box lid removed, main jet #142m needle +.030, pilot jet was fine with stock, mixture screw backed out 2 turns. This really woke the bike up. "Unplugged" as they say. I did not have any of this smog stuff removed, I quest the technician did not see the need.
In this case I do not think that a horsepower rating gives the whole picture. I think that torque tells the story. When people ask me about the mods and what I think, I say the bike seems to have a lot more torque. Thats just me.