so here's the backstory. 81 xs650 that I purchased not running and missing a few pieces. I've been putting it back together for a couple of months and recently got in running. it runs like garbage. low compression on the left cylinder around 100 psi. right is 125-130. left cylinder seems to be running rough, stumbles and pops. right cylinder is better but backfires into the air filter occasionally. mixture is obviously rich. plugs are black, exhaust smells like fuel. carbs have been rebuilt and I put pod filters on, so bumped up the pilot and main jet one size as a place to start. had some exhaust leaks because of a bad muffler install, fixed that. runs a little smoother now, but right cylinder seemed to have not been firing at first, but it caught on later. dosen't idle well and often dies. adjusted the cam chain tension yesterday and got that right, it was way loose. i can hear what seems like a leak from the intake valve when i turn the crankshaft with a wrench, but i'm not sure. today I cracked it open to adjust the valves and right off the bat, the intake valve on the bad cylinder is jammed down so it's not flush with the top of the spring. basically I can't even get a feeler gauge in there to check the clearance. also looking through the spark plug hole the intake valve appears to push much further down than the exhaust valve does. here's the valve from the top: here's the intake valve open inside the chamber: so what do I do to fix that valve? Do I have to pull the engine and tear the top end apart? my guess is it's not seating right which explains the bad compression.