Guys, recently picked up a super clean 09 KLX250S in Red. Sweet bike, and I have read nearly a year of posts on this board to see what if any issues I should keep and eye out for and to learn what the best mods are. Man what an outstanding resource! Thank you...

So on to my question and idea about the exhaust. Has anybody cut the stock 09+ exhaust apart, or know if the tiny little exhaust tip is the main restriction?

If so, I was thinking of machinging something like this for the 09+ exhaust. I have a CNC machine and enjoy projects like this.



I have a number of mounting ideas, so that shouldnt be an issue. The big questions is whether opening up the exhaust directly in the back will help flow and performance.

Most are going to ask, why not just purchase an exhaust?? Honestly I dont mind the cat, and it being a clean burning machine. Being quiet is my preference as well.(man I must be getting old!)

David

 

The OEM exhaust is really heavy too. If you like quiet and the cat then just leave the exhaust alone. I have found OEM exhaust systems to be pretty good over the years. No need to repack, usually built better (ie, the OEM exhaust bolts to the frame in more places), and is quieter. Quiet is good.

You want more power? Save the pennies for a big bore kit.

For some more flow without having to buy an aftermarket exhaust you can always remove those two drain plugs.

 

Can you improve the performance of a stock muffler by modding it, sure. Can you get the performance a good aftermarket piece will give you, no.

 

Thanks for the input... Gives me a few things to consider.

From reading the board, stock exhaust will support 18-20hp at the stock displacement. Given the diameter of the stock pipe outlet(tiny) just increasing that outlet a small amount will increase the area/flow significantly without increasing sound much. I dont think one would need to increase flow much to support the 3-4 additional HP the stock displacement is good for.

Cats are one of the best mufflers you can find for reducing sound but allowing great flow if designed right.

If anyone has a stock 09+ exhaust you want to sell cheap so I can experiment, let me know.

David

 

Soudns to me like a waste of time, but if you're into projects like that - it's your bike, go for it!

 

I cut apart my stock exhaust and made the outlet from 15mm to 21mm. It seemed to work for me. Still quiet but lets more air pass through a bigger hole.

The one in the first post looks LOUD.

I will post pics lately.

I like keeping the cat. Just my opinion.

I do have a second stock exhaust.

David

 

djb - you'll see lots of old posts of folks drilling out the small hole. Some have said that ruins the spark arrester, which is a no-no for many off-road riding areas.

 

anyone know if the klx 140 pipe will fit the 250????

 

David, I say go for it. You may have just hit on a 'in between' mod that there may be a market for. I would bet you dollars to donuts that people told Bill Blue that a big bore kit was a waste of time too. If you can come up with a cost effective mod, BINGO! Good luck.

 

Your HP numbers are way too optimistic, stock the bike runs 17-18 rwhp, A real good stage 2 bike with after market pieces and proper jetting might get you to 22 or 23 rwhp. With the stock pieces in place I would expect less that half of the increases obtained with good aftermarket stuff.