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Discussion Starter #1
I am rebuilding my 250x and I have access to a 05 300ex crank. Will this be a viable swap without any mods? If it will swap out, do I need to use the 300 counterweight? Any input much appreciated, just thought it would be a easy way to get some extra stroke.
 

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I thought of doing the same thing but I'm going to have to say there may be some interference issues. even though the only difference is the stroke and elec. start of course I think I would give it a try if ypu don't mind tearing it down again if it don't work. or just go to www.powroll.com They sell a +12 Stroker kit bumping the 250X up 100CCs
 

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Discussion Starter #3
thanks for the input trx2five0. i am like 95% sure it will work. honda moved the connecting rod "big end" farther from the crank center line and used a shorter rod to give the 300 more stroke, as far as i know the 250 and 300 pistons will interchange, meaning that the piston pin placement is the same for both pistons.
east coast of nc? i lived close to wilmington for 5 years, when construction went belly up i moved back home to the mtns.
 

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I would think you would need the counter balance shaft as well the difference in the strokes wouold throw it off. I know what you mean about the construction industry, I work in the rental industry and we feel the hit too.
My question is why are you doing the crank swap? you can achieve the same CCs or clos to it by larger piston. Besides these 250 will out run a 300 if they are built right.
 

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Moose is right.If you have a longer stroke there is more of a chance of breakage.
 

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Discussion Starter #6
that is a good point. what i had in mind was giving it a little extra stroke by using the 300 crank and then by boring the jug out it should put me close to 300cc's. i was going to use a 11 to 1 piston by wiseco. maybe go with the milder powroll cam and have them hard weld my rockers to match the cam. I have a newer model 300ex carb which is 32mm. i have a cobra exhaust, and two different fmf exhaust. one of the fmf has a open end on it and the other has disc like a supertrapp. i feel like this should give me good power and keep good reliability. I may be totally off base, i dont know. i am new to this game. which of the three exhaust would be the best for power?
 

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Well I am sitting right at 288CCs without stroking the crank 80mm 12:1 piston. FMF and HMF make real good power the 3003x carb is no different than the 250X actually smaller the 250X carb is 36mm if you want to make better power step up to a crf250 carb or a 400EX carb. the best on to have is a flat side.
 

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Discussion Starter #8
thanks for the input moose. Just to let everyone know for sure. the 300ex crank is not a direct bolt in. the shaft on the left side for the flywheel is longer on a 300 because of the electric start. the crank bearings are also a little bigger. The right hand side of the crank, the clutch side, is the same. So to use the 300 crank in your 250 you would have to change crank bearings and use the 300 flywheel and left side cover and delete the electric starter. as far as electrical, i dont know. u know how this stuff goes sometimes, one problem leads to another. Moose, what kind of gas do you run with yours being at 12:1? i have to drive like 45 minutes to get racing gas.
 

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we have a couple of places here that sell racing fuel and the airport sells 100 low-lead. I run racing fuel 93 octane mix 4gallons racing fuel 1 gallon 93 octane it cost me about 40 bucks to fill up my 5 gallon can. I try to run straight race fuel but I mix it to save a few bucks. it will run on high octane but not as well as race fuel.
 

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Man moose you spend alot on fuel.I only run 93 octane.And a question.Does the crf250 carb give you any difference?I mean like jetting or air.What mm is it?
 

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I would think it would make a difference. I'm not sure about the mm ours is 36.. the 400ex is 38mm and they do make a difference, I'll change out mine when I put my ported head on. Not sure which route I will take though?

CRF250 Carb


400EX Carb
 

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Well hope it works good for you.
 

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i dont know it may out run some 300 but not mine
 

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You only say that because you 700 miles away, trust me little buddy this 2FiveO is bad A** and I haven't even put the head and carb on yet.
 

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i not saying that i know there bad quads but the 250x is meaner
 

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i slow lol i talken about the 250two stroke is mean to
 

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yah they are but there no mach to my dads 525 or my cuz 660r they raced them b4
 

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Bull 300.I bet you moose's 250 would whoop your 300ex(330ex).And a 250 r with a good pipe would beat a 660 or a 525.I've seen it done.
 
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