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1998 KX 250 Top End Rebuild

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I finally got fed up with my bike smoking like a freight train along with its lack of power, so I tore into the motor yesterday. The motor has supposedly been bored 40 over by a previous owner, and it looks like the cylinder has been re-sleeved. I have no experience whatsoever with two-strokes, so maybe some people can help me out? Why would the cylinder have been re-sleeved if the bike was bored over? Is that done to get it back to stock cylinder diameter? The exhaust valves were extremely gummed up also.

I'm wanting to run a setup that will give the bike more than enough power for woods riding and some steep hill climbing (I don't want to be bogging down when I'm almost at the top of a hill). I also would like a setup that is reliable when cranking. I want the bike to crank consistently on cold and hot start ups.

So, what machine work should I have done to the cylinder, and what type of piston and rings should I go with? Are there other things I should do while I have the engine torn down?

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I finally got fed up with my bike smoking like a freight train along with its lack of power, so I tore into the motor yesterday. The motor has supposedly been bored 40 over by a previous owner, and it looks like the cylinder has been re-sleeved. I have no experience whatsoever with two-strokes, so maybe some people can help me out? Why would the cylinder have been re-sleeved if the bike was bored over? Is that done to get it back to stock cylinder diameter? The exhaust valves were extremely gummed up also.

I'm wanting to run a setup that will give the bike more than enough power for woods riding and some steep hill climbing (I don't want to be bogging down when I'm almost at the top of a hill). I also would like a setup that is reliable when cranking. I want the bike to crank consistently on cold and hot start ups.

So, what machine work should I have done to the cylinder, and what type of piston and rings should I go with? Are there other things I should do while I have the engine torn down?

Your cylinder was sleeved to allow the useage of Wiseco pistons. I am no fan of Wisecos, as they do nothing for added power, or performance. The do however offer the advantage of "overboring" in the event you badly sieze a piston. You need to take your cylinder to a shop and have them "mic" the cylinder to see if it's within tolerence. If not, I think you are screwed, as .040" over is as far as you can overbore your cylinder. You will need to install a new sleeve, or purchase a new nickasil cylinder from Kawasaki. As for your power valves, in the future run a good full synthetic premix oil mixed at 42:1, or 50:1. You won't have any more gumming up of your valves.

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I'm looking to make the bike dependable and with great performance from the motor as well. I would also like the bike to be able to crank with the least amount of kicks possible. I'm more than likely going to have the cylinder dipped and then re-sleeved. So what are some good piston combos to go with (brands, sizes, etc..)? I'm looking for ideas from you all if you were also having to rebuild your top-end and you wanted it built for the same type of riding I do.

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