Ok so I read this tread and I just HAD to register too reply.
To answer a few ?'s
1. "does wiseco make 240 kits"
NOT really but they do sell a 240 piston and sleeve (but the sleeve is made by L.A. Sleeve not wiseco) so in a way they kind of sell a 240 kit.
2. "Can you bore a stock cylinder to 240"
NOT really. you cant bore it that big. (that would make the walls of the cylinder too thin.) you can however have the stock cylinder sleeve pressed out and have a 240 pressed in making the stock cylinder you once had a 240 beast.
3. What companies sell a 240 kit?
Theres more out there than have been listed. they are Trenga, Vitos, Planet blasters (phantom), CT's, Snyder Motorsports, Diamond racing, L.A. Sleeve Just to name a few. As per which one is better vs. Junk is really a matter of opinion.
4. "Do they over heat"
Done incorrectly yes they can. but if the shop doing the 240 kit is reputable you can have a reliable 240 for quite some time. However there are newer options out there that will give you closer HP output too that of some 240 kits with out going the 240 route. Ive got CT's ultimate 240 kit have not had any overheating problems as of yet. Dont forget though, with any motor mods, you need to have the right combination of parts/service done to your machine to achive maximum performance/reliability.
One thing too keep in mind is that the ATV racing industry is a small world. Dont be supprised to find out that many competitors use each others products and or services for their own purposes and actually collaberate with one another. An example is the CT 240 kit I have is actually produced by L.A. Sleeve. but CT buys them and dose some reworking of the ports and sells them as their own kits. L.A. Sleeve is the major manufacture of Sleeves and many many companies buy and use there sleeves. they kind of have a monopoly on that, per say.