Im trying to find out if the big bore kits from the 300ex will fit on a '87 250x? I have heard both yes and no,want to make sure before I buy.. Thanks

 

I would think the best way to find out would be to call the manufacturer of the particular kit.

 

yes a 300ex big bore kit will work on a 250x . The 300ex and 250x share the same top end the only difference is in the crank . The only difference would be the displacement for example if you bought the 330 kit ( 80mm piston ) for a 300 ex and put it on the 250x it wouldnt be a 330 it would make it a 288 because of the different crank.

Google powroll.com They sell pistons and bigborekits for just about any fourstroke and they have a lot of info about 300ex and the 250x


hope this helped

 

Yes. The bores are the same, the stroke is different, so the kit will work.

 

Im looking at this kit,the seller says he doesnt think itll work on the 250x..I was under the impression that if it fit a 300ex it had to fit the 250x...
It should fit, right?

Honda 300EX BIG BORE KIT W CYLINDER - eBay (item 290488081737 end time Mar-14-11 05:36:31 PDT)

 

Yes it will fit . With the big piston be sure to replace your timing chain . It seems like a good price .

 

Before I order it,one more question..

Will the big bore 250x have more power then a piped 300ex? How much?

 

That's a good question. I know stock they are pretty much dead equal because the 250X will rev to higher RPM's because of the shorter stroke. If I were to take a wild guess, I'd say the 300EX with a pipe would have a little more power BUT BUT BUT, you have to remember that the 250X is more than 20 lbs. lighter. (351 vs. 373). That's a lot when you take it as a percentage of total weight. About 6%. Not so much if it were a 4,000 lb. car but we're tralking light weight ATV's here. I've always been a 250X fan.

 

If your bike is running good I would leave it alone . If your goal is to out run a 300ex with a pipe there may be another way . A big bore kit will have a different power curve than a stroker motor . Thats why the new fourstrokes are so fast they are stroker motors . Everybody use to install the biggest piston they could in their bike to get a lot of cc's . The bikes had lots of torque but didnt rev very fast . Now fourstrokes are made with a stroker crank and have the same cc's as a big bore kit but with a smaller piston it c.an rev faster and makes a completely different power curve . With a big borekit your bike would be around 288cc's . A 300ex is 282cc's but because Honda went with a stroker crank instead of a bigger piston I think the 300ex will be a little faster because it will rev faster but you will be able to pull some killer wheelies .

Back to your bike if you install the big bore kit you will also need to get a better exhaust system so the new motor can breath . Posiibly a cam , definitely a new timing chain and a good air filter ( K and N ) you could be looking at a lot of money just to ourun a 300ex . If this is your goal my 1st question is how long of a race are we talking about ? 300 ft is the typical race on a drag strip but if your looking to outrun the 300ex in a big field with room to stretch out a little ( 1/2 mile ? ) then you can change the gearring on your bike . This would be alot cheaper than a piston kit . You can also change the gearring for a shorter race

I love the old 250x I ride a 250x with the 350x motor but I have had alot of 250x bikes . I drag race mine in ohio on a 300ft drag strip . I was outrun last year by a 250x stroker bike but a lot of that was the gearring I had and the fact my bike stands straight up on the starting line . I am playing with my gearring a little and installed some taller rear tires for racing. If I were you I would buy an exhaust first with a good head pipe , re jet the bike to make sure you getting a good fuel mixture ( dynojet kit $44.00) change your airfilter to a good highflow filter and then see how good it runs . If you need to rebuild you bike I would look for a 11 to 1 wiseco piston and maybe bore your cylinder . And buy a hotcam off ebay ?

A word of advise someone will always be faster than you but ask youself is it worth having a bike that goes fast in a straight line that you cant ride in the woods because it will over heat ? The guy that outrun me had over $1200 in his motor with a $500 curtis spark exhaust but he can only ride his bike on a drag strip because it will overheat . With that being said I am trying to find a way to outrun him this year so NO !! I dont listen to my own advise .

I hope this helps good luck with you bike

 

Hey BIGBOREKIT, what you said is directly the opposite of what I said. I was always taught that if 2 engines have the same cc's, but one has a shorter stroke and bigger bore than the other, the one with the shorter stroke and bigger bore will rev higher.