1978 Mercury 50hp having issues yet again

[KevPool]

Hey guys got her running great for the past month or so and have really learned the inns and out of this old engine since I got her,,,, but today I'm stumped,,,, we took our granddaughter out for her first ride today and we had a blast the boat ran great for the whole afternoon. Little gal wanted to stop and do some fishing so I dropped anchor and we sat chilling out fishing for a good hour or so, pulled up anchor and went to head back to the boat launch then things went south. We didn't even get up to plane and the boat lost all power and I had to troll her along the river to get us home. So here are the details of the river run. Ran great for a few hours had her WOT till a fast plane then 1/4 back as always stopped did our fish then started up and this issue happened. Got her home checked the filters on the carbs no gunk at all, fuel was fine as I have two tanks and even switched it out on the river just incase fuel was the issue. Did notice oil residue on my bottom spark plug threads. I haven't torn it apart that much yet but beer is in the fridge and I would like to be on the water tomorrow for my birthday so any quick tips would help.

 

[Texasmark]

Ignition coil. May not show up again till it gets hot. Pull the plugs and clean them off with a shot of Brake Parts Cleaner and reinstall. If it starts and runs go for it. If it quits again, pop the cowl, pull a plug, put the cap on it, touch the case of the plug to the engine block and roll the starter. If no flame I'd go for a bad coil/ magneto, whatever you want to call it that generates the high voltage to the plugs.

 

[jimmbo]

Verify that the spark can jump 7/16" gap on all cylinders. You said there was oil on the bottom plug threads. Both bottom cylinders or just one? If both, then the bottom carb might be flooding