Getting a old Mercury to run isn't always easy. You can have 120 psi compression, great spark and a good carburetor and a mercury still may not start. A mercury has ball and roller bearing on the crankshaft and it needs a good oil seal on each end of the crank to hold crank case pressure. Over time these seals get hard and won't seal. The seals are available but a little difficult to change.
Mercury -MK20, MK10, KH7, KG7,KG4, KE4,KE4, KE7, KF5,KF3,KE3,KD4
Wizard WH7, WD4
Johnson - QD15, HD26, TD20, KA38
Sea King 5, K1 (merc)
Evinrude- Foldlite 1930, ELTO - LW #309, 1951- 7.5, Zephyr, 68 3 hp
Bendix SMD , Champion 4.2 , Scott 7.5,