Hi I'm new here, Great site. Last season my engine fried a couple of pistons, 3 tanks of fuel later same thing. Replaced the pistons again and checked over everything I could think of. I'm suspecting the high altitude compensator were the trouble as I found moisture, ice, water in the hoses. Disconnected the system and vented the carb bowls to the atmosphere, plugged the vac. now it runs better. My jets are stock 390's, seems right according to the charts for our riding conditions. I was wondering if I should change jet size???? Both meltdowns were at WOT. Any thoughts will be appriciated, Thanks in advance

You could check the rubber carb flanges for cracks and crank seals for air leaks

Oh yes, As 720 said, remove those carb boots that hold the carbs to the engine and check them for hairline cracks!! Look them over GOOD!! I had a '94 ZR 580 and I had to replace the boots every year almost!! Those engines really viberate and cause the boots to crack alot!! My stock jets were 400 and I put in 360's. Ran real good but I took it easy when it was real cold!! Check those carb mounts!! Rammer!!!

Check those carb boots Newfie EXT.
or next time, don't drive WOT. LOL.

Thanks for your input, greatly appriciated. I,m going to have a closer look at those carb boots now. My cousin call last night, when he fired up his ZL500 everything inside the mag was lighting up and it's loosing fire. but thats another story!! Thanks again.