Re: 1971 Mercury 800 thunderbolt
GET a dial indicator, remove all the plugs, install the dial indicator into #1 cylinder remove the little plate on the top of the distributor rotate the flywheel clockwise until #1 piston pushes dial indicator all the out this is TDC; now on the belt drive pulley on the top of the distributor there is an arrow make sure that the arrow is pointing perfectly towards the center of the crankshaft if the arrow is off one tooth one way or the other you need to re-align the belt. You have to be close now or the motor would not even start.
Then goto the timing testing and adjusting section in the manual and start from the beginning. setting the primary pickup, then primary to carbs then max spark, then secondary pick-up and finally max throttle stop. If any of these are off the motor will run bad. You say the plugs are wet are they wet with FUEL or WATER. Are they droplets or even coverage of soot, carbon or oil fule mix.
Aim Outboards and Machine