Motorcycle Repair: Banshee cylinder boring, oversize pistons, head gasket

Question
I own a '97 Banshee that I bought used in 2000 with the stock factory motor in it, and melted the left cylinder piston, which wore a groove in the cylinder wall. I'm pretty sure the groove is small enough to bore out the cylinders and install oversize pistons without having to resleeve the cylinders. I've heard that on some of the model years, Yamaha nickel plated the cylinders, and that nickel plating can't be bored. Is that true, and does the '97 have the nickel plating? Alot of people tell me that bike engines will still run well even with sloppy cylinders, but since I'm doing the work on it I might as well do it right anyway. Also, the main jet needle for the carb on that cylinder was so gunked up that when I took it apart a couple months before the piston melted, I almost couldn't pull it out of the venturi chamber. That cylinder, (the left one), also seemed to burn a little more oil than the right side. Before I cleaned the carb up, the throttle would stick wide open from time to time when the bike got wet,(going through puddles, streams, etc.). After I cleaned the carbs up, I thought that would solve the sticking problem, but it didn't really. I always ran a 25:1 fuel ratio as the Yamaha manual suggests, but after being asked by EVERYONE that I knew who ever owned a two stroke why I wasn't running 32:1, I decided to run that mixture. I ran maybe 1 1/2 to 2 tanks at 32:1 before the piston melted. However, the top of the pistons don't look like they were running too lean. If anything, it looks like they were running too rich. Dark black, but the left cylinder is pitted, kind of like small craters on the top of it. Also, the last two times I rode I blew a lot of steam (NOT oil) out of the exhast while blasting up long hills. The stock head gasket appeared to be in good shape when I pulled the motor apart. Does that give you any clue on why the piston fried? Outside of that, I'm kind of amazed at how well the motor has kept together. (Crankshaft to rod clearence, clutch plate thickness, gear teeth surfaces, etc.)
Thanks in advance for any info you can give me. I'll be checking my e-mail for a reply.

Answer
Hi Dave,

I would have to inspect the engine to determine the cause of piston failure.

I'm not sure about the cylinders on the '97 YFZ350. I don't rmember and I cannot find anything about them being chrome plated (nikasil) type cylinders in my resources.

It is normally difficult to detect visually in a used cylinder if it is chrome plated or not.

If any doubt exists, a solution of copper sulfate (CuSO4), which can be purchased at any drugstore or chemical supply house should be applied with a cotton swab to an area of the liner. If the liner is not plated, a copper color will appear. If it is chrome plated no change will take place.

Visit these sites for more about tuning your Banshee:

www.dfn.com/benkaren/jetfaq.html

www.atvfrontier.com

www.yamaha-motor.com

www.bikebandit.com

Send me your email address as requested. I'll return a few tech files. AllExperts doesn't share email addys with their experts.

Respectfully,
Mark Shively