2000 XL 1200 LTD - Riva stage II + R&D M16 reads,dominator manifold,48mm carbs, with RIVA gas operated power valves. The carbs are set 130 low speed jet,1 turn on low speed screw, 160 high 2 turns out - 2.5 needle with 115 gram springs.
I have been though 2 rear cylinders and three pistons in the last year.There is a whole burned into the top of the piston directly under the spark plug which runs towards the exhaust port. I called R&D and was told Yamaha had a problem with the manifold sealing to the cylindars and water was being drawn in which would cause the piston to burn. I found the bolts in the manifold were bottoming out in the holes. I shimmed them with washers and really tightened them up also using Yamaha black gasket sealer. This appeared to help but, I have now burned another piston. Any suggestions would be greatly appreciated.

sounds like more of a lean condition then water intrusion

any sugestions on jetting size? I have read a couple of e mails on this on your web sight one was the same stuff I have 140 low and 165 high would .05 really make that much of a difference?