IS IT POSSIBLE TO PUT A 350X MOTOR IN A 250X FRAME? IVE HEARD THAT IT CAN BE DONE. HOW MANY MODS WILL I HAVE TO MAKE? AND WHERE CAN I FIND A 350X MOTOR? ALSO HOW MUCH WILL THE MOTOR COST ME?
IS IT WORTH THE MONEY OF SHOULD I SAVE THE CASH AND BUY A 400EX?

 

Powroll makes a kit to put that engine in there. I believe with their kit it is a bolt in with very little mods. You will need to get an exhaust done for the dual port 350X exhaust.

This is what I would like to do, but need to find a 350X engine.. I know K&K has them, but I dont want to shell out that kind of cash, I am hoping ot find one that needs a rebuild and then get osme work done on it.

 

I mounted my 350x motor in my 250x. I did it myself with some help from an old Dirt Wheels. You will have to shave and shim a few mounts to fit the frame but because the cases come from the same family of engines, the bolt pattern around the circumference of the case is the same. To mod the exhaust, I had to cut the stock Y pipe from the 350 (about 1" from the head flange) and weld in some extensions (about 1" to 1-1/2"... can't remember) to get it around the frame. I also had to cut and weld an extension on the 250 silencer between the can and where the two come together. You will also have to make a few mods to get the two to mate up. I've been running it like that for about 5 years and no problems. I have rebuilt the engine once to a higher compression piston and cleaned up the bore. As to where to get one(a 350x motor), you will have to look around at scrap salvege yards etc... you can find them, I just picked up a whole 350x bike (motor in a box... broken valve) for $150 Canadian (approx $5 US) I just happened to be at a bike shop looking at used sleds and saw it sitting in the back. I'm gonna BUILD the engine and rebuild my Old 350x from the better parts from the two of them. If you check out www.powroll.com or call 1-800-powroll, they can set you up with all kinds of info on rebuilding your 250x, 300ex, or 350x, lots of different combinations for rebuilds... Good luck and keep the rubber side down....

 

I have a 350x engine in a 300ex frame(same as 250x). I put it in myself. It wasn't any trouble.
I used the original 300ex muffler extended the header pipe two inches to clear the frame, and had a muffler shop make a short pipe to connect it all together. You need to use the 350x wiring harness.
So if you buy just a engine, buy the wiring too.

 

Oh by the way I put a 10.5:1 Wiseco piston in mine and it is killer to kick start!

 

According to Powroll, all you need is a 350X engine, CDI box and a 250X with a wiring harness which would mean you use the 250X wiring with the 350X box....