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CRF250 road race mods

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Hi All,

Thought this would be the place to ask around. I am planning on building CRF250 motor for road racing. What mods should I be looking for, and what power levels can I make reliably? Happy with high maintenance, but I would like to get an entire race meeting out of a motor (4 days). Sorry if this seems like a simple question, I am coming from 2-stroke world and I know a few people here might have played around with this idea before.

Due to frame restrictions, I cannot run the EFI motor, so that limits me to 2009 or earlier I believe (correct me if wrong).

Cheers

Edited by username_01

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Not familiar with your intended usage,

but I'm thinking a CRF250X with it's wide ratio gearbox might be better suited for your project.

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 you'll be running near the rev limiter for extended periods on that little 250! Balance/blueprint the motor will help it survive. I road race a DRZ400 with the AFM and I know several guys running 450 motors but haven't heard anyone using a 250 4 stroke single. You can do a lot to get more top end from it...head work, cam, ceramic bearings, micro finish gears bigger carb.. I'd be worried about reliablility at those high rpms...but I think you'd be able to get several races out of it for sure...I did over 1000 track miles on my DRZ last year without any issues.

10645196_4529275525703_6692234752042406756_n.jpg

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I sponsored a road race team with a 2014 EFI motor and the kid won the championship. When geared up on the countershaft, the mx gearbox spreads are perfect. If you find that you can use an EFI motor, or complete bike, shoot me a PM and I can help. He didn't have a mx bike chassis, some sort of tube chassis with fairing and all.

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Far out cheers guys. havent checked this website in a while and came back to this so thanks for the info!

bike is Gp-Mono. 250 4 stroke single cylinder - these were the predecessor to the current moto 3 class while they were phasing 2 strokes out. Not a moriwaki md-250  though, my bike is slightly different and a bit rarer. I've a rolling chassis, but no engine yet.

They originally ran the 250x motor, but with the R transmission and cylinder head. I will be buying a donor bike, keeping the engine and selling the rest. Plan so far is to swap out the transmission for the close ratio R box, put on a ported cylinder head and cam, race fuel, and full-rebuild from ground up as a minimum. Looking for mid 40 hp.

I am hoping someone can give me some advice on who to send the head to, and possibly what parts to try. So far I have only heard of Ron Hamp however I understand he is a busy man.

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On 6/4/2017 at 0:43 AM, username_01 said:

Far out cheers guys. havent checked this website in a while and came back to this so thanks for the info!

bike is Gp-Mono. 250 4 stroke single cylinder - these were the predecessor to the current moto 3 class while they were phasing 2 strokes out. Not a moriwaki md-250  though, my bike is slightly different and a bit rarer. I've a rolling chassis, but no engine yet.

They originally ran the 250x motor, but with the R transmission and cylinder head. I will be buying a donor bike, keeping the engine and selling the rest. Plan so far is to swap out the transmission for the close ratio R box, put on a ported cylinder head and cam, race fuel, and full-rebuild from ground up as a minimum. Looking for mid 40 hp.

I am hoping someone can give me some advice on who to send the head to, and possibly what parts to try. So far I have only heard of Ron Hamp however I understand he is a busy man.

Call Mummert. http://www.ford-y-block.com/atvkits.htm

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Wish you could use the EFI engine i have one hear that is built up to the botom new crank super finshed trans with 3rd 4th gears under cut falicon rod  have nt bought a piston yet but have a fully ported 2016 head with bronze alloy intake seats 25 mm buckets my rhc .5 mm orver intake valves .

 

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1 hour ago, Ron Hamp said:

Wish you could use the EFI engine i have one hear that is built up to the botom new crank super finshed trans with 3rd 4th gears under cut falicon rod  have nt bought a piston yet but have a fully ported 2016 head with bronze alloy intake seats 25 mm buckets my rhc .5 mm orver intake valves .

 

Hi Ron, I wish I could use EFI too, but I think I would have to modify the frame/airbox. As they didn't make many of these bikes (26 or 27 from memory) and I don't really want to modify it if I don't have to. For those interested, there is a good link to a series of images which show what these bikes look like when done.

http://s266.photobucket.com/user/mickeydainish/library/Harc-Pro 250 GP-Mono?sort=3&page=1

Beautifully made, a lot of hand welding and fabrication. Best swingarm I've ever seen on a smaller capacity bike.

 

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Well i can help on the build i had done the top end on one that the late Tryce welch built i think it was for Lewis i know it beat the aprilia 125 2 stroke in florida 

 

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Hi All,

Thought some would appreciate an update on this.

Bike is together (see images) with a 2006 CRF250 R motor. I also have custom shafts (which were made by Harc Pro in Japan) to run the R gearbox in X cases if I ever want electric start.

The valves in the engine are pocketed, so some work required. The only question is what to do? Does anyone have any recommendations to make the engine reliable, rather than chasing outright power?

IMG_7486.jpg

IMG_7493 2.jpeg

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Hi All,
Thought some would appreciate an update on this.
Bike is together (see images) with a 2006 CRF250 R motor. I also have custom shafts (which were made by Harc Pro in Japan) to run the R gearbox in X cases if I ever want electric start.
The valves in the engine are pocketed, so some work required. The only question is what to do? Does anyone have any recommendations to make the engine reliable, rather than chasing outright power?
IMG_7486.jpg.1c13c9a7c4d6967657b111080e656599.jpg
1927351160_IMG_74932.jpeg.c26be25fcb6b94290e1074f4216a2fe9.jpeg
Ron can help you with the motor, but I would be more worried about how to keep your front wheel out of your radiator during the entire suspension stroke...

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41 minutes ago, Eddie8v said:

Ron can help you with the motor, but I would be more worried about how to keep your front wheel out of your radiator during the entire suspension stroke...

Yes - looks odd but is the same geometry as any 125 GP/moto3 bike.

honda-rs125-gp-luyten-kitted-nx4-race-bike-2.JPG

Kalex-moto3_stripped-2snap_lowres.jpg

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