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Discussion Starter · #1 ·
I've owned my 2003 klx 110 for about 15 years and have put countless hours on it. The bike still runs although feels like it only has about 2/3 the power it had when I bought it. Also it does not idle at all. I've gone through multiple parts of the bike and still have not fix these problems. I've thoroughly cleaned the carb and adjusted idle and air screw as well as replace pilot screw one size bigger. Also cleaned the air filter and disassembled exhaust. After going through the bike I've come to realize that it probably needs a top end overhaul (piston, rings, gaskets, pins). I've checked the parts sources online and find the parts are very reasonably priced. Some questions:

1. Should I do a compression test before tearing the top end apart?
2. Is it common for these cylinders to need to be resized or honed? I've replaced top ends on other bikes but wasn't sure what type of metal they use on these cylinders.
3. What's the safest way to ensure I get the correct oem piston size? Vin #? Measure the piston itself?
4. How extensive is the job? I did a big bore kit on an xr 50 years ago and it was more complicated than a 2 stroke top end but I still got through it. I'm guessing this job is in the same ball park.
 

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Then I'd say it's time for a new top end, especially if you haven't done it since you've owned the bike.

Are you looking to keep it stock(ish) bore or want to upgrade to a big bore kit?
 

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If you're keeping it stock, you'll need to have the cylinder mic'd and bored for an oversize piston from Kawasaki.
 

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Discussion Starter · #6 ·
Yes, I’d liked to keep it stock. So I’d have to buy a piston (preferably oem) and send it somewhere to have the cylinder bored to the exact size of the new piston?
 

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So I’d have to buy a piston (preferably oem) and send it somewhere to have the cylinder bored to the exact size of the new piston?
Either that, or have a local machine and/or speed shop measure the bore of your cylinder, and then you order the one you need. It appears that there are only two overbore sizes available from Kawasaki, as seen HERE
 

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First do a compression test if you like but I would go ahead and replace your rings anyways. Then Youtube how to time in a KLX 110, that will help you with the tare down and replacement of the upper end gaskets. You want to use a micro tool to check out your bore to make sure it is still perfectly round and not oval. If it is still perfectly round then check the cylinder jug for gauging and light scratches if any. If you find any imperfections and you can feel them with your finger nail then it will need to be bored but if you can see light scratches and the cylinder is still round then use a honing tool with some oil and polishing blades till the light scratches are gone and then recheck the cylinder for roundness again after your finished. If everything checks out then replace your rings, put on your lower gasket, the cylinder jug, then the head. If the cylinder is oval then you will need to have it bored to fit the 138cc piston or buy a 143cc big bore kit with a 60mm piston and a Mikuni 26mm carb. You can use your stock head with these parts but it will increase your compression and make it much meaner then stock. I used a YX160 cylinder with the 60mm piston with a 13mm wrist pin, 55mm crank, 26mm Mikuni carburetor, and a stock head on my 2003 DR-z 110. She runs amazing. The difference between the YX160 jug and the 143cc big bore jug is the YX has a steel sleeve and the 143 is aluminum. I hope this helps you and good luck with your build.
 

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Discussion Starter · #9 ·
Thanks for the responses guys. Wonder if it would be easier just to start with a new cylinder with matching piston rather than trying to spend the money and trouble to refurbish the old one?
 

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Yes, It would be much easier to just replace the cylinder and piston ring set. You should be able to buy a stock cylinder jug for your bike at TBoltusa.com and that way you know everything is good. You will also need a top end gasket set, a stator cover gasket and some Honda bond gasket seal. If you go with a different size jug like a 138cc, 143cc then you'll need the piston to match and a new 26mm carburetor setup for the 143cc. Good luck and happy riding.
 
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