Pulled each plug wire, and it dies with one, no change with other. Getting spark to the bad cylinder. Pulled valve cover, everything mooving as it should. Checked valve clearances - they were a bit big, so changed them but did not fix. Pulled plug on bad cylinder, and its dry...shouldn't it be wet after running? Took carb off and dissasembled and cleaned. At the end of my rope Oh yea, started doing this 2 weeks ago, then ran OK since. I put a bottle of marvel mystery oil in fuel and its been fine until today. Any ideas?