The 40HP CRF250 Dual exhaust mod
 

A lot of people commented on my duals here, and other riders on the road nearly fall of their bikes trying to look at how these MX exhausts were bolted on so I must have done something right.... or wrong. But here's the rought install procedure. Remember, my bike is 95% tarmac and street, 5% gravel, 0% playing in knee-deep mud. BTW, the exhaust sounds MX and awesome, it will also allow flow worth 40HP.... but you will not get anywhere near 40HP from doing this ... unless God sends me some kind of super head with super cams to match my 350cc big bore....

What you need: CRF dual exhaust and mid Y pipe, a chopsaw, file, metric ratchet set, an ring-type slip-on exhaust gasket to fit between header and CRF Y pipe, appropriate jets or pumper carb, 2 small to medium size stainless fuel hose clamps that fit into the CRF silencer mounting holes (or make silencer mounts).

Carbs: You need either a pumper carb or mod the stock carb. For pumpers, I recommend FCR37MXs, easy to get on ebay. To mod the stock carb, remove the hose that goes between carb and airbox. Install an open-air filter on carb and jet appropriately.

Relocating the battery: Remove rear plastics and seat. Remove complete stock exhaust. Remove everything inside the airbox till the battery fits, my battery wires will fit without modding. The rear battery frame will need to be cut off to install exhaust, those concerned may need to get a another brace bracket made that fits the CRF exhaust.

Mounting the exhaust: Cut slotted part of the stock header off. Test fit with CRF exhaust, it will be too loose. Get ring gasket to fit between header and Y pipe. Mount the header with bolts loosely, slide in Y pipe from wheel well, and hose-clamp silencers in appropriate locations. Do what you need to do to clear the airbox.

See picture for reference, mine is still about 1 inch too far back since I used an aftermarket header. When I fix it, the silencers should be more hidden inside the rear fenders.

Looks good man. Way too much work.... lol.

Very impressive and a tip of the hat to your work there. The Honda 250 that the exhaust came on was designed with the volumetric efficiency to work with that system...but you already knew that. As you say, our KLX's will probably never achieve that kind of volumetric efficiency to match that setup. Additionally, didn't Honda abandon the dual pipe setup on later models? Please understand that this is no slam your efforts here. The cool factor and uniqueness is indeed impressive. I wouldn't do it to mine, but it's the kind of stuff I enjoy seeing industrious people accomplish.

this post is useless without a video with sound :-) ...

...and more pictures

+1...

+2...

I do like those rims though. Where did you put the radiator resivor? Eliminate it?

You will find my water reservoir is in pic

My engine is taken apart for more porting and new cams, video coming soon after I get the cams in....

BTW, can you upload vids directly here?

Relocate the battery? To where?:eek: