CRF 250 PROJECT

Brian Degulis · Posted: Fri Nov 30, 2012 7:16 pm Post subject: CRF 250 PROJECT

I'm putting together a CRF 250 4 stroke shifter. The goal is to do this for under $4000. I've purchased a used (new top end) 2006 CRF 250 R engine. I've got a line on a roller or may use one I have. I'm planning to modify the bike exhaust and use it. I will buy or make a mount.

Does anyone have an idea of gearing?

Does anyone know if the cr 125 engine sprocket is the same spline as the CRF 250. I've been told it is but would like to confirm.

I'll need a shift lever any ideas?

Any ideas on starting? I'm thinking the 4 stroke might be hard to start with a belt? What about leaving the kick start in place.

Brian

Jeffrey Clark · Joined: 16 Oct 2012 Posts: 3

My CRF 450R is a kick start dirt bike. On a bad day kicking that will wear me out. Finally got jetting right but still these engines can have a mind of their own until you get the starting routine down. Pull rope won't work though. Too much compression. Plus when the engine is hot the bikes have a hot start lever you pull in that changes carb settings temporarily to make starting the bike easier, with the kickstart, imagine the difficulty in a pull rope.

If you did this you would want to leave room for that kickstarter, and run the hot start cable to the lever also, mount that where you can kick and pull the lever in at the same time. I will say I don't use my hot start lever very often, but when I need it, it does make the difference in making the engine easier to start. Usually on 90 degree or hotter days. It usually takes 1-3 kicks to start it when warm, and 3-6 to start when cold. On average, this is normal for 450's, 250's are probably the same.

Chris Reinhardt · Posted: Sat Dec 01, 2012 4:32 am Post subject:

Sprockets I believe are different, shifter I think is the same as the CR125/CR250. Worst case on the sprockets, weld a 428 to a stock CRF.

Get in touch with someone from Honda HPD, they put a kit together for the FI CRF250 with sprocket adapter, mount etc, I'm not sure if all of that will fit your motor.

On the starting side, we modify the CRF450's to use an external starter like a Coleman or a Burris type, fires right up every time, never used a hot start, barely used the choke. I would imagine it could be done for the 250's as well.
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Brian Degulis · Posted: Sat Dec 01, 2012 6:22 am Post subject:

How do you modify them for a coleman starter?

Brian

Chris Reinhardt · Posted: Sat Dec 01, 2012 6:36 am Post subject:

Brian Degulis · Posted: Sat Dec 01, 2012 7:35 am Post subject:

That's slick but it looks complicated. How is it done?

Brian

Chris Reinhardt · Posted: Sat Dec 01, 2012 9:54 am Post subject:

I weld a plug into it and I have a fixture for the 450's that I use to locate the hole and bore it. Then I weld a 17mm socket to the crank gear bolt and turn it down in the lathe. Cut a pocket for the seal, done.

Unless you're pretty good at Tig welding aluminum, and the casting is pretty darn clean, I would not suggest doing this at home....

But it's the way to go, I would never start one any other way, unless it had on onboard starter ie, an X model...

CR
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Howie Idelson · Posted: Sat Dec 01, 2012 11:03 am Post subject:

17 tooth drive gear will be good for any sprint track.
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paul rees · Joined: 06 May 2007 Posts: 264

Chris Reinhardt <<< Chris I am glad your company can do these types of Mod's . But it would be nice if in the future, that you not use a photo of my engine and frame in your show in tell's . And claim as examples of your work. My Clutch cover was not Mod'd by your company . But it was done by Flat Track Engine Machine Shop Specialist. This cover type of work was done for me at a big discount. Because he was interested in my project. And no that is not a cut down socket in the photo ether. Paul

Brian Degulis · Posted: Sat Dec 01, 2012 11:33 am Post subject:

Very slick but a procedure I don't want to get into right now.

What about welding a fixture into the axle bore on the engine side to accept the starter shaft? The obvious problem is that your loosing torque to the crankshaft because of the gearing but I wonder if it would work in a high gear?

17 tooth is good for 2 stroke but this is 4 stroke operating at a lower RPM with more torque I think?

Where should I pick up a pulse for the fuel pump?

Brian

Howie Idelson · Posted: Sat Dec 01, 2012 6:53 pm Post subject:

17 tooth like I said. And yes for the 4 stroke. I built one myself and drove it a ton. Trust me. Pulse line goes in the side of the intake just like a 2stroke.
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Brian Degulis · Posted: Sat Dec 01, 2012 7:36 pm Post subject:

Alright what's a starting point for the rear?

Side of the intake meaning what? 2 stroke gets a pulse from the crankcase on the 4 stroke clone it's of the valve cover what do you mean by intake?

Brian

Howie Idelson · Posted: Sat Dec 01, 2012 8:58 pm Post subject:

Look at a stock moto. The pulse line is drilled and tapped into the side of the intake track. Very simple. Stuff a rag in there and drill away. Rear gear starting point 24 or 25 doesn't really matter - the power is so much wider then the CR, the gear isn't nearly as critical..
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Brian Degulis · Posted: Sat Dec 01, 2012 9:50 pm Post subject:

Alright Howie believe me I'm not trying to be a pain I'm just trying to understand it because I'm going to be doing it. The way I understand it the intake track on a 2 stroke is thru the crank case. On a 4 stroke it's not. So are you saying get the pulse somewhere between the carb and intake valve or from the crank case like a clone. If it's crank case then wouldn't the valve cover be best to avoid picking up oil in the pulse line? Also did you use a Y fitting and return line from the pump out put to the carb or just go with a single line?

Brian

Howie Idelson · Posted: Sun Dec 02, 2012 7:50 am Post subject:

Right. Between the carb and the reed cage on the seat side. You won't get any oil in the pulse line. Yes, run a Y fitting and a line back to the tank. Round Mikuni pump works great.
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