Welcome to YAMAHA chief! I am an old YAMAHA service mgr and Technician, these skis are horrible for this problem!! 99% of all piston failure is due to lack of lubrication, you cant check the oil pressure with ya hands! you getting ready to spend alot of money on fixing this ski! YAMAHAs arent cheap to work on, you need to fix the engine then rebuild your carbs, do not skip the carbs!!! then you would be wise to mix your oil!!