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250x big bore

  #1  
Old 03-01-2011, 11:38 PM
Weekend Warrior
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Default 250x big bore

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
 
  #2  
Old 03-02-2011, 12:05 AM
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I would think the best way to find out would be to call the manufacturer of the particular kit.
 
  #3  
Old 03-02-2011, 04:20 PM
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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
 
  #4  
Old 03-03-2011, 06:11 AM
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Yes. The bores are the same, the stroke is different, so the kit will work.
 
  #5  
Old 03-03-2011, 10:22 AM
Weekend Warrior
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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)
 
  #6  
Old 03-03-2011, 04:03 PM
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Yes it will fit . With the big piston be sure to replace your timing chain . It seems like a good price .
 
  #7  
Old 03-04-2011, 02:00 PM
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Before I order it,one more question..

Will the big bore 250x have more power then a piped 300ex? How much?
 
  #8  
Old 03-04-2011, 03:12 PM
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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.
 
  #9  
Old 03-05-2011, 05:33 AM
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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
 
  #10  
Old 03-05-2011, 08:02 AM
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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.
 

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