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Just picked up an 07 crf250 roller and i have a spare 96 kdx 200 motor freshly rebuilt so me thinks a hybrid needs to be done.
Its a twin pipe model and im thinking i will need to reduce the diameter through the pipes? any ideas? Will put some pics up soon as, thanks.

http://s1207.photobucket.com/albums/bb462/cj555rally/

cj555rally wrote:Its a twin pipe model and im thinking i will need to reduce the diameter through the pipes? any ideas?

If I'm understanding this correctly, you can't (well I guess you could if you want the engine to run like garbage) use a 4 stroke pipe on a 2 stroke. You'll need to figure out how to make a KDX (or similar) 2 stroke pipe fit.

Tedh98 wrote:

cj555rally wrote:Its a twin pipe model and im thinking i will need to reduce the diameter through the pipes? any ideas?

If I'm understanding this correctly, you can't (well I guess you could if you want the engine to run like garbage) use a 4 stroke pipe on a 2 stroke. You'll need to figure out how to make a KDX (or similar) 2 stroke pipe fit.

Guess i didnt explain too good! I mean using the crf silencers. I have a DOMA expansion chamber i can mod to fit but was wondering if i needed to reduce the silencer id as 4 strokes are bigger or just find a couple of 2 t silencers? Just thought it would be different to have twin pipes.

Gotcha.

2 strokes are sensitive to exhaust changes. I'm thinking that anything you do that takes you too far away from the stock based set-up is going to hurt performance more than help.

But if you don't mind spending time and some money trying to make it work, you don't have much else to loose.

I'm not sure if this makes sense, but I'd find out the ID of the KDX silencer and then find tubes 1/2 that diameter for each CRF silencer.

I wouldn't bother with the dual silencers. Use one 2t silencer and a KDX pipe.

"I'm not sure if this makes sense, but I'd find out the ID of the KDX silencer and then find tubes 1/2 that diameter for each CRF silencer."

To be precise, (not that I think it'll matter much) that won't be the same, check your math, you'll see it doesn't add up

scheckaet wrote:"I'm not sure if this makes sense, but I'd find out the ID of the KDX silencer and then find tubes 1/2 that diameter for each CRF silencer."

To be precise, (not that I think it'll matter much) that won't be the same, check your math, you'll see it doesn't add up

Yeah, there was absolutely no engineering or math behind that recommendation.

yeah I figured.
(for example) if the kdx id is 40 mm, to get the same surface with 2 pipe you'd need 2 pipe with ID of 28.28 mm.

Hmmm, maybe the con's out weigh the pro's here. Think i will concentrate on getting the motor and expansion chamber installed then decide on silencer options. Thanks for the input.

i remember ages ago, when i was in my early teens, i used to put around town on small 50CC 2strokers
DTRs, TSXs, MTXs, that sort of things
anywho, there was a local partshop who carried dual exhausts kits for these 50cc bikes and they may or may not have been made by a company called "proma"

(did a quick search and also found a guy with a firebox dual exhaust)

http://www.brommerforum.nl/gallery/view/2139/2/3

cj555rally wrote:Hmmm, maybe the con's out weigh the pro's here. Think i will concentrate on getting the motor and expansion chamber installed then decide on silencer options. Thanks for the input.

Yes you need to concentrate on the major frame mod. The frame Y will need to be cut and relocated higher for clearence of the pipe at the exhaust port exit.

Another issue is whether you heat treat the area after you weld said Y piece in. I don't know if will be an issue due the KDX motor not having insane power, but once aluminum is welded is loses strength in the area of the weld.

Heat treating, or the lack thereof, shouldn't be an issue. Guys over at KXrider have done plenty of KX500af conversions with no heat treating and having no issues.

Not heard of anyone heat treating after welding and have read a fair few project threads on various forums? When i have welded it all up and done all the other little mods im sure it will need i intend to have the frame and swingarm powder coated. This will involve heating but not to a high enough temp to alter anything i would guess??

The crf250x uses the same swingarm as the 02-newer cr125's so the rear mount and chain alignment should be a piece of cake.

marrk_us wrote:The crf250x uses the same swingarm as the 02-newer cr125's so the rear mount and chain alignment should be a piece of cake.

The bike is a 250R not an X. Are they different?(swingarm)
Anyway got it mostly stripped last night so will find out pretty soon.

^no

All good info guys, will have some pics tomorrow. Thrown the engine in place,Y needs to be moved a fair way up! Easter holidays now so should get a good few hours on it over the weekend....

marrk_us wrote:The crf250x uses the same swingarm as the 02-newer cr125's so the rear mount and chain alignment should be a piece of cake.

My bad, missed it wasn't an X. Still takes the same pivot bolt so hopefully the rear alignment will be as easy as mine was.

marrk_us wrote:

marrk_us wrote:The crf250x uses the same swingarm as the 02-newer cr125's so the rear mount and chain alignment should be a piece of cake.

My bad, missed it wasn't an X. Still takes the same pivot bolt so hopefully the rear alignment will be as easy as mine was.

Not at all, lot more of you guys over the water with good info. I thank you all......