86 Merc 115 runs poorly then clears up

[Volphin]

I ran into a nasty problem with my dads 86 Merc 115 today. Took out the boat for a fishing trip and she started hard. Then she quit. Got her restarted and headed for the channel. (I have a trolling motor so if it failed to start... no biggie if I'm close to the dock.) Opened her up a bit and she was bogging down BADLY. Max RMP was 2900-3000. She felt like she was missing on a few cyls. I slowed down a bit and tried to go to idle. She stalled and would not restart. So after trying to crank her with coke on, off and any way I cold think of, I just let her sit for 15 min or so while I fished.

Finally got her started again and took her for a little run. She was bogging and then she cleared up and ran normally. I wonder if the carbs need rebuilding or if one is flooding? Or maybe its an ign issue. I'll be looking at her closely next weekend as I had guests this weekend at the lake house.

Oh, and if this helps, she was making a banging noise every once in a while like someone took a hammer to the lower unit, or shot it to put it out of her misery. LOL

VRO is full of oil and bulb is primed nicely. Gas is fresh. Just looking for a starting point so I know what tools to bring down next weekend.

 

[Mi duckdown]

Do a compression check.

 

[Chris1956]

Inspect or rebuild the fuel pump. If the fuel pump diaphragm leaks, raw fuel will cause her to load up. That banging is a bad sign.....

 

[Volphin]

I had a chat with dad today. He mentioned that he was on the lake when the low VRO oil alarm went off. He stopped the boat and checked the reservoir, but it still had plenty of oil in it... almost full. I wonder if the VRO is going south. Anyone have a diagram of this system and common fail points? I'm thinking that this could be the issue...