Dead Cylinder?

Very first thing--I guess you did--look at the valve action,

second is a compression test and maybe a leakdown

Not having a leakdown, you CAN just rig a fitting to an air hose and pressurize the cylinder, then listen for bad leakage at the carb throat and exhaust.

Is it using oil? Any possibility it has some broken rings, or someone LEFT OUT the top ring?

Are you sure it's not a plug? (Don't just go by the looks) Swap a known good plug, known good wire, make sure.

Know how to do a simple "cylinder balance" test? Just pull up the boots on the dist, then use a probe to ground out each wire. You'll quickly discover which cylinder(s) is not firing