Hey, y'all, don't know if this might help anybody, but at least you might find it entertaining....
About 3 weeks ago I found a 300EX on Craigslist for a decent price. I went and looked and saw the clutch cable was about wasted (easy fix) and it had some minor issues like the rear caliper dripping brake fluid, but nothing serious. Cranked right up, went in all 5 gears and reverse, had plenty of power. After a little back and forth, I got the quad for my price and headed home.
When I got to the house and backed it off the trailer it wouldn't crank, but I figured it was probably out of gas and rolled it under the carport. The next day I go out, it spins over fine, but won't even pop. 3/4 tank of gas and I know it was getting through cause I could smell it. Ignition, I think and got out my trusty spark light. It's got fire. WTF?
SO I say, well, the only other thing it can be is compression. So I pull the plug, put my thumb over the spark plug hole, and spin it over. Son of a bitch, it wouldn't even push my thumb off. No compression.
So it drove me crazy all day, how did it run so good last night with no compression? At the bike shop when I'm ordering my new clutch cable, I tell the parts guy my story. I said "I guess when I get home tonight, I'm gonna pull the head off and check the rings and piston."
"You check the valves?" he asks.
"No."
"Check the valves," he says. "That's what I'd do first."
So the next day I pull the plastic, tank, and inspection covers off, and check the valve clearance. OK on the exhaust, but couldn't get the smallest feeler gauge I got between the tappet and intake valves. I set all 4 valves to .10 mm, reassembled, and hit the starter.
WHOOOOOOOOPOPOPOPOPOPOP!" runs like a top.
Moral of the story: check the valve clearance first.