Kaw650sx

Hi guys, got a question for you advanced ones. I just bought a 91 Kawasaki 650sx and my buddy before me was having problems with it blowing head gaskets. I did a ton of reasearch and went thru the thing pretty well. I pulled cylinders off honed them, removed the studs to convert to a bolt setup, had the head milled and also the top of the cylinders(very minimal amount, just enough to have a zero deck- had about 165 compression), reringed the pistons, replaced the plugs and replaced all gaskets. Blew thru all the cooling hoses to make sure of no blocks, and even added a slight amount of oil to gas just in case the oil pump didn't work correctly, plan on blocking off. Had it running pretty well up at the lake in and out of the water, rode for about 2 hours, water would sizzle on head. Brought home, had it sit about a week, and took to the lake this monday. Ran about 5 min. and blew it up. Melted the head into one of the cooling sides, and blew out the gasket, Cylinders are fine and pistons move good still, cylinders seemed dry. I guess i am wondering what is still causing all of this even after my rebuild, cuz the problem still persists. Am i running really lean? Is it my carb? Do i have an air leak somewhere? Any help would be greatly appreciated. Thanks Ryan

no fear here

The only thing that comes to mind is, do you have the cooling hoses routed properly. If you dont this would cause the motor to overheat. The jet pump is designed to pressurize the cooling system from one fitting, and another fitting is designed to create a negative pressure for the factory bilge.

Also make sure that the cooling hoses running under the hood are all run properly. Does it have an aftermarket exhaust, this will sometimes change the configuration of the cooling lines under hood. If so you will have to search out the manufacturer to confirm the hose routing.

You have already done everything that I would have up to this point.