Sport 400 Melting Pistons

[TimVDB]

97 400 Sport eats pistons like there candy. Just got it and took it for a ride and she melted the piston. Found out she had straight water in the cooling system so assumed it froze and ran hot. It was 25 degrees when she ate the piston. I rebuilt the motor, put anti-freeze in it and she ran great-till she ate that piston (about 10 miles each time). Melts the piston on the exhaust side until a hole is melted thru the piston. The injector is adjusted slightly over (rich) factory setting and I added 2.5 oz's of oil to the gas for break-in. Has Aaen pipe into a DG silencer. D8EV plug. Was going 40+/- steady throttle when she got hungry. Fuel acts to be on the lean side but throwing plenty of oil at her. Might not have been re-jetted when the pipe was added????? But, runs strong w/ no popping or backfiring usually associated with a lean burn. What do you think guys??

Tim

[Demon Rider]

Well if you got antifreeze in her instead of water then you cant blame it on the cold temperatures. Is the exhaust valve have carbon blocking the flow of exhuaust valve? Is the timing correct? Has there been any engine work done so that the piston is too big for the cylinder?

[TimVDB]

2 stroke Demon-No Exhaust valve. There is also no type of "power valve" on the exhaust side. I'm leaning toward a leaking crank seal(s).