Been working on getting my 1986 Mercury 8 for about a month now. I had an issue with spark and fuel at first and have fixed those issues now. Its got new spark plugs, new switchboard, cleaned and resealed carburetor, new impellor/water pump, and new lower unit oil. I FINALLY got it to fire after replacing the switchboard and spraying fuel into the cylinders the other day. However, today I dropped it into the water to try and run it off of the carburetor but now I cant get it to fire at all, even with spraying fuel into the cylinders. It still has STRONG spark, just wont fire. Here are my thought, sheared flywheel key, flooded, or possible broken reed valves (even though they are brand new, maybe broke when I got it to fire??), or lack of compression.
