Help with my 1982 Mercury Outboard

[MadCityBoatGuy]

I have a 1982 Mercury Outboard 35 Hp on a pontoon boat. The motor has been running pretty well... until... last weekend we had a pretty large group on the boat, and took it around the lake for a solid 45 mins at med/high speed. Everything was going great. Then we stopped to swim for maybe an hour and a half. The boat wouldn't start again. Eventually I was able to get the boat to run at high idle, but as soon as I tried to push it into gear, the boat died. What is also weird is that the boat starts really rough. It used to start just fine. Now when I get it going (it usually takes a couple tries) the boat in neutral goes like crazy. I gets super loud and seems like it is going to explode, then it usually slows down and dies.

Any ideas?

 

[jimmbo]

Well I would really like to see a pic of your engine, as there was no 35 hp in 1982.

"the boat in neutral goes like crazy" well two things, it really needs to be in gear to go anywhere. Revving the engine like crazy in neutral is quick way to blow it up. High revs and sudden throttle closings also cause engines to fail from suddenly getting very little oil. High revs in Neutral, mean nothing as the engine isn't under load, you can have a dead cylinder and it will still rev in neutral.

First thing to do is a compression test if acceptable, check spark plugs, and check to see if the spark can jump a 7/16" gap, then check for adequate fuel delivery to the carbs