Japan may have rules or laws that don't encourage large displacments I have no idea but just the fact they aren't over there means nothing really. I bet there are things in Japan that you can't find here and that's ok too.

 

Of course there are rules, one specific rule makes the availability of big bore kits all the more inviting. Bikes up to 250cc are not subjected to any kind of yearly inspection. So any bike which has a big bore kit fitted is VERY unlikely to ever be detected, especially with 0.249l written on the cylinder.
As such a 315cc kit, fitted to a road bike, is technically illegal, but widely available. Probably with the disclaimer that they should be used for off road only (but are not).
In fact I've seen many KLX's for sale with the standard 292cc kit, still registered as 250's, no one bats an eyelid.....
That's why I wondered why they stop at 315, when the market for bigger is clearly there.
Rules don't come into play here, big bore kits are available for all bikes.

 

So has anyone sent their cylinder to get done or do they just get him to ship one he has? How does that work is it cheaper if I send him mine to get done? Refundable core charge of 175? Not fully understanding this part?

 

You're sure right about some of the neat bigger bore kits available for all kinds of bikes and scooters over there in Japan. One guy in my area had been trying to get a 160cc kit for his 125cc Yamaha Zuma scooter that he had read about, and he finally got one. They may have more big bore stuff over there than we have available here.

 

Core charges are common place. How it works: If you have the time, and want to send him YOUR cylinder, he'll put a new sleeve in yours, and send it back when he's done. Some people would rather do all the work at one time, and in that case, you add 175.00 to the price of the kit, and he sends you a cylinder with the new sleeve in it, as well as the rest of the kit. Once you are finished with the swap-over, you send him YOUR cylinder, and he'll send your 175.00 back to you.

 

Oh, ok I get it. Thanks

 

Ok another question....has anyone drove the 331 and the 351? Probably not but just checking. Just wonding how big the difference really is

 

Mathematically, assuming 100% benefit per cc difference, it's about 6% more potential power to go 351.

 

Save your money and do the work yourself. Do a search & read up on all the installation threads on the websites. Get familiar with the pictures, get ahold of a service manual study up. Two strokes bikes/atvs were the only thing I had experience on, but I tackled the job. Its not hard to do. Ask any questions here, lots of people to help out. There is a good sense of accomplishment when your done that can't be beat. The money you save can go torwards a pumper carb, instant throttle response is a big benefit.

What I read was on jetting go up 2 sizes on the main jet and 1 on the pilot jet, with the cvk carb. I had to rejet bigger for the big bore kit with the pumper carb. Bigger displacement = more heat, keeping the lean jetting from stock is asking for trouble. Remember the big bore sleeve is thinner to fit into the stock cylinder opening in the cases.
Heat warp that and your screwed.

 

Ya thats the kind of crap I am worried about....the wall being so thin with heat and such. But other people have it so it must be ok. I'm still not sure if I have my carb set right now....lot of popping on decel but thats another story.