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07 cr250 Jd jet kit or keihin pwk

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Setting the squish clearance is only part of the equation. You will also need to machine the dome, or the compression ratio will be wrong. You will need to cc the head to maintain the correct trapped volume. Squish angle and width is also important. This exceeds the scope of expertise available at most local machine shops. Send the head to RB and have the job done correctly.

:smirk::banana:Great advise.

The angle of the squish band (05-07) is shallower than the angle of the dome of the piston. If you just tighten the squish not only will the comp be too high but the difference in the angles causes a pocket of trapped gases at the edge of the piston causing detonation.

It really seems like Honda rushed this engine into production. It seems like they had the engine designed with a flat top piston then at the last moment switch to a dome piston & just added some squish clearence & pushed it out the door.

Edited by gospeedracer51

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The angle of the squish band (05-07) is shallower than the angle of the dome of the piston.

This is correct, at least on my '06. There was actually a slightly negative taper to my stock squish with refrence to the piston dome arc. RB cleaned up the whole mess and it now runs and jets worlds better than stock. I still have more work to do, but this engine responds very well to mods and has tons of potential if properly set up.

Edited by APBT

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So you will spend $75 on a jetting kit, and $100+ on a carburetor, but not $75 on setting you squish clearance? :p:smirk:

Your jetting will be WAY more consistent after setting your squish, which is the MAIN contributor of the problem you are facing.:cheers:

http://www.rb-designs.com/

:smirk:

So, have you had the squish clearance set on your bike? I have an 07 CR250 and will probably haver to do the same to mine. Do you know a good mechanic, or have any measurements so I can give my mechanic some idea?

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Yes.

Go here ------------>http://www.rb-designs.com/<-------------------------

On the left menu click "Head Mods".

In the third line is a link "Squish Band Clearance Test" click it.

I would do the procedure outlined there and send my cylinder head to Ron of RB Design and have the squish set for $75 + $15 for shipping and handling.

:smirk:

So, have you had the squish clearance set on your bike? I have an 07 CR250 and will probably haver to do the same to mine. Do you know a good mechanic, or have any measurements so I can give my mechanic some idea?

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Setting the squish clearance is only part of the equation. You will also need to machine the dome, or the compression ratio will be wrong. You will need to cc the head to maintain the correct trapped volume. Squish angle and width is also important. This exceeds the scope of expertise available at most local machine shops. Send the head to RB and have the job done correctly.

I appreciate your thoughts and concerns. but i have my full confidence in this machine shop to do what needs to be done. my father and i have done business with the from forklift motors all the way to semi motors and they specialise in everything. plus the fact that i could have my head into the shop and back in less than a day and be riding seems alot more reasonable than sending the head via mail

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JD Jetting sells the pwk that will fit your bike and it comes with his jet kit already installed..

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I appreciate your thoughts and concerns. but i have my full confidence in this machine shop to do what needs to be done. my father and i have done business with the from forklift motors all the way to semi motors and they specialise in everything. plus the fact that i could have my head into the shop and back in less than a day and be riding seems alot more reasonable than sending the head via mail

You are planning on having a diesel engine shop work on your CR250 engine? That's a very bad idea.

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I appreciate your thoughts and concerns. but i have my full confidence in this machine shop to do what needs to be done. my father and i have done business with the from forklift motors all the way to semi motors and they specialise in everything. plus the fact that i could have my head into the shop and back in less than a day and be riding seems alot more reasonable than sending the head via mail

Do as you like. It is your bike, your head, and your money. However, I know what I would do.......

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You are planning on having a diesel engine shop work on your CR250 engine? That's a very bad idea.

they arnt just a diesel engine shop. they do motorcycles,top fuel drag racers, and everything inbetween. they have all the equpment needed to do the head mods.

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Do as you like. It is your bike, your head, and your money. However, I know what I would do.......

i understand what you would do. and im not denying your advise, but I like the thought of having my bike apart in the shop and back in the cource of two days at most. it seems easier for me right now

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they arnt just a diesel engine shop. they do motorcycles,top fuel drag racers, and everything inbetween. they have all the equpment needed to do the head mods.

Top fuel engines and motocross engines are apples and oranges. Having the equipment is only part of the equation. If they don't work on motocross engines every day, they probably don't have the technical data required to make good modifications to your CR250.

For head mods, you should use a shop that specializes in motocross engine modifications and has experience with your particular bike model.

I would recommend Eric Gorr. www.eric-gorr.com

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i think after all I will go with rb designes, like you have said i would rather have it done right then have it done cheaply.. so rb head mod and jd jet kit sound good

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i think after all I will go with rb designes, like you have said i would rather have it done right then have it done cheaply.. so rb head mod and jd jet kit sound good

Well done. Now go to the www.rb-designs.com website and closely follow the instructions for measuring your stock squish clearance. RB will use the solder measurements that you supply with your head to perform the required machining. Since you are using an '07 head, do not be surprised to see a large stock squish clearance. Mine required a call to RB for advice on an alternative solder part number to take the measurements. Tell RB wether you plan to use pump fuel or race gas as this is also a consideration. Precise measurements on your part will result in a higher quality end result from RB.

RB told me that he has seen better results with the Keihin PWK AirStriker than with the Mikuni TMX on the CR250. You may want to discuss this issue with him as well. It may be a better option for you to get a Keihin from e-bay than spend a similar amount of money on the JD kit. However, even with the stock Mikuni- jetting will be easier and more stable with the RB head.

Edited by APBT

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you could go to motocrossgiant.com they sell the keihin 38mm pwk airstriker with the jd jetkit preinstalled for $245.95. and it comes with extra jets and needles. i bought one and i dont know how i ever put up with my mikuni.

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I have a stock motor 2006 CR250..................I had the RB head mods for pump gas / then put on a 36mm Keihin from a 2011 KTM250SX , with JD jet kit installed.

The bike runs great !

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you wil be chasinbg jetting ghosts with the factory carb and lousy factory squish in the head, send it to rb or eric gorr to have it corected. I think its worth doing the head and pwk, after what the boyesen is great on the cr250.

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