i am having trouble with my 1978 mercury model 200 20hp. Serial range 4709593 and up. I aquired this motor from an old fire department that rarely ever used it. the guy said maybe 30-50 hours on it. paint is still on the prop and fin. It has been sitting in a garage for 20 plus years. Once i got my hands on it, every wire was dry rotted. So i got a print out of the diagram from a local marine place and rewired the entire motor. once rewired i rebiult carb, water pump, new foot oil and seals. Once complteded i could not get the engine to idle so i took it to my local repair shop and it ran good for a few weeks. Then the problems started! when running wide open, it seemed to lunge back and forth and seemed to hit full then 3/4 throttle back and forth in about 1.5 - 2 second intervials. I assumed this was a spark plug problem and did not think about it. once we sit around for awhile the motor would not start. the best way i know to describe it was it souned like a lawn mower with a weak battery. I tried to pull start it but could not turn the engine over with my rope. I finally got the motor to crank with the throttle wide open and made it to the truck. I did notice that there was a steady drip of water coming from the top spark plug threads. Could this be water in the piston causing to much compression seeing as how i could not pull start it? i have ordered a new gasket for the spark plug cover. Does anyone know if this will help my problem? when i took the plate off i noticed the plugs thread into the actual chamber. i also looked real hard with an LED light for cracks in the head and could not find any. Any help would be great!!
