Check the fuel lines. If you have the old gray merc hose it could be the liner has broke down due to ethanol fuel. If the plugs are dirty replace them , not a big expense. No sense trying to diagnose an outboard with bad plugs. After that determine if you have a fuel or electrical issue. When in doubt separate motor from boat. My best suggestion would be to purchase a REAL Mercury service manual. Do not buy an after market one.