Low Speed Dim Spark

[MMcrack]

This is my first write-up so lets see how it goes...

I recently purchased a 1986 Mercury Classic 50(45). when I bought it we started it right up with muffs and it sounded great. Upon leaving there and getting back home I took the boat out to the water and immediately started regretting my decision. The motor started up great and runs okay at slow speeds....but that's as far as it goes. At WOT it only goes 7MPH. So me, being the troubleshooter that I am tried to figure out what it was....here's where I'm at now..

First and foremost; the compression on all 4 cylinders is between 118 and 120.
When pulling the spark plugs i have found that the top two (cylinders 1 & 2) are a bit dirty and wet. the bottom two (cylinders 3 & 4) are for the most part clean and dry but still a bit wet.
I'm getting spark on all 4 cylinders, HOWEVER on 3 & 4 its just a faint spark when using an inline tester. Cylinders 1 & 2 produce a bright blue/purple spark.

Swapped spark plugs between 2 & 3: produced same results.
Swapped spark plug cables: produced same results.
Swapped ignition coils: produced same results.

Now I'm lost... Could it be a stator? Is there a way to test it? And would this be the reason the boat only goes 7MPH? Could it be the switchbox? is there a way to test that?

Any ideas are greatly appreciated!:help:​

 

[MMcrack]

For anyone that has this problem, here was my solution...

After searching and searching all over the engine to find answers as to what the problem could be, I found out that the trigger had one wire that was completely corroded and another that the insulation was coming off. this was causing them to short on each other thus causing erratic sparking on the bottom two cylinders. I ordered a new trigger and installed it. It was still only firing one two cylinders so I played a "move the wires around" game and came to the final conclusion that my switch box was bad. it was getting power to it, but not sending it to the plugs. Upon ordering a new one and installing it, my motor now runs perfect and speeds down the river at 32MPH!