yamaha 250 ox66

[unimat]

I have a Yamaha 250 ox66, facing a problem with the lower cylinder. After i change the spark plug the motor runs well, after 20-30 hours of running the cylinder starts cuting out and i find salt on the spark plug, I changed the lower crankshaft bearring,oilseal, we planed headset, and replaced headset gasket, but the water still goes in.
could you give me any suggestions, what else to look for?

[jb123]

what year and have you looked at the water jackets??

cracked block or water in fuel

[jb123]

ooops my bad, dont think the jackets could let in water but if its not coming in from fuel, a compression test should show a deficiency.

[unimat]

thanks for your reply, it's 1998, I didn't check the jackets yet