Mid 80's 50 hp mercury issue

[jmd1]

Hello, have a coworker that bought a 15 ft larson boat with a 50hp mercury2 stroke on the back. He took it out this weekend, put in water started and took off. Out of wake zone, they advanced throttle with no response. He said it was doing around 8-10 mph total. Unsure of rpms, if they came up or not.

Anyway, once they ran for a while, pulled to shore, pulled plugs top two look like new, bottom two are black with carbon. He dinked with it for awhile spent the day on the lake, running it on two cylinders.

He has no clue where to start, but after I did some research sounds like the cid box could be a common issue as could the coil packs.

Anyone have thoughts which way to lead him?

I don't have serial number etc, but can ask him. Thanks Jeff

[Rick G]

I can't see two coil's going out but I guess it could happen. Does each plug have spark? Could be bad switch box, I can't remember if they had one or two on the 50. Could also check the top carb to see if it's getting fuel. Might want to check compresion on all four cylinders too.

[boatfixer]

1 switchbox on those and I would lean towards that. 2 clean plugs while 2 are dirty is an indication of no spark. Has he checked for spark?

[jmd1]

Not yet, he is not that mechanically inclined so i offered to get some info for him. He is a temp employee so cost is an issue. i suggested that he check for spark, even move the coil packs to see if the issue moves.

I will tell him again that he should do the spark test first and then possibly move to the switch box. Any thoughts of possible damage to the engine for running it like he did? Thanks again for the help folks, this board is great for this stuff. Jeff