What should I do soup up my 250x engine or should i find a good 350x engine to put on my 250x frame? On my 250x everything is stock but k&n airfilter and fmf powercore. I can beat 300EX's but i want to be able to beat some 400EX's. Please give me your advice what i should do.

 

first advise is to search the forums!

lots of info there

the 350x is a popular conversion

me personally..........i would rather just have the whole 350x and sell the atv

 

This is a question I had asked myself about a month ago. After doing some pricing I have opted to finish hopping up my 250x w/ a 80mm 288cc big bore kit ($300 from 4 Stoke Tech + $150 for resleeving and boring). If I get the stroker ($350-$500) it will be 352cc or if I get a 300ex bottom end 330cc. With these mods, mid-range cam, high lift spring kit, high strength cam chain, ported exhast, large port racing carb(2mm bigger than stock eliminating the accelerator pump), K&N filter, and my big bore kit I should be able to run with a stock 400ex or maybe even a piped one. Which is not bad, but with those mods that is about every thing that can be done to this motor. So now with stripping it down to the frame last night to powdercoat I'm starting to wish I had spent the $1,000-1,500 to go with a 350x motor. At first the modded 250x may even be faster that the stock 350x motor or the same but with the 350x motor I could mod it out to 498cc and never have to worry about power again. I have heard though that there is a crankcase problem with the 350x's, also I would have to have gotten a custom exhaust for the front between the motor and frame. I have also heard that the '86 is a better motor that an '85.

So it is basically a money decision you have to make. If you have to slowly make upgrades to the 250x motor or shell out $1,000-1,500 for a 350x motor.

D@#%! Sorry to be so long winded! Hope this helps.

 

Two of my buddies have 350x's for sale for 900 dollars. Complete bikes. If you want more info e-mail me at badboyzracing_99@hotmail.com

 

It depends on how much you want to keep reverse. I would go with the 6 geARS then reverse.

Get a 350x and do an XR500 head conversion

 

Good point THEXOTIC1! Lots of power there with the 350x & 500xr head conversion! With the head conversion you have to machine the case. Another thing I forgot to mention is you would also not have reverse with the 350x. Also that when adding the stroker to the 250x big bore kit the gearing is not strong enough and the clutch will have to be redone.

Maybe I could do the 350x head with 250x bottom end (300ex would be better) machine the case halves and have reverse too! Hmmmmm.

 

We had the 300ex big bore 405. You will have to change sprockets to find the correct gearing.also the clutch will have to be beefed up. We ran a 14/34. or 15/38 with 18inch rear tires. Also the 250x head will not fit on a 250x/300ex.

 

What do you mean "Also the 250x head will not fit on a 250x/300ex."? I would hope the 250x head would fit on a 250x and the 300ex is the same motor just stroked different.

 

OK, I'm sure you meant 350x head does not work with 250x/300ex. Thanks, I was wondering about that. Where was the problem at or just all around won't work?

 

yes i meant 350x head will not fit 250x/300ex lowers