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Kx250 big bored. What's the biggest I can go?

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I have a 1999 kx250 and my cylinder is getting pretty worn out and am thinking about sending it out to get bored to fit an oversized piston. I was wondering what's the largest the cylinder can be bored and what displacement will it created. Biggest piston I've seen is 68.50mm (stock 66.40) with a displacement of 265cc.

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An extra 15cc's is just not worth the trouble.  Stock size parts are easy to find and cheap. 

Do some port work and get the squish set and it'll run better than an ordinary 265 will anyway.

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Where can I get in contact with this company

He's a member on the forum, he doesn't sell big bores. Eric gorr makes a 265 and 295 big bore and it comes ported to what you want. I have his 265 on my kx with more better porting and it pulls harder everywhere. I believe the 300 and 310s are sleeved.

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He's a member on the forum, he doesn't sell big bores. Eric gorr makes a 265 and 295 big bore and it comes ported to what you want. I have his 265 on my kx with more better porting and it pulls harder everywhere. I believe the 300 and 310s are sleeved.

I know very little on porting. Where can I have it improved and what does it do to the ports

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Changing the ports changes the power characteristics of the engine. I've used Eric gorr on the kx, it's included in his big bore. lots of people do it just research them.

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Port timing and size can be changed to make an engine more suitable for a specific purpose.    Usually the head gets worked on to compliment that too,  though not always desireable.  Lots of butchers in that business.  EGorr is reliable and I have found him honest.  Start into it with a real goal though.   And remember, you can't really have "everything".  I would avoid any of the kits where they sleeve the engine with an iron or steel liner.   I have yet to use one that has an aluminum liner so I can't comment on them.  15cc's alone isn't worth doing a big bore,  but if you are looking for lower end it can be noticeable.  Not so much for the increase in displacement,  but it now makes the carburetor seem "smaller" (leaning it out probably required).  It also lowers your transfer ports when the cylinder wall is cut away.  the port roof angle is for all intents 45 degrees,  you cut back into that .040 each side.  Amounts to lowering the cylinder .020" where the transfers are concerned if you leave it that way (kawasaki literally did just that with the kdx 220 by boring the 200,  and the kx100 by boring the 80/85). Of course the ports can have the original timing restored or beyond too for that matter.    So think about it before you do it.  

Edited by ossagp
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