Got a mercury on a pontoon boat. In idle it revs up and runs fine. Put it in gear and under load and it bogs down and won't open up. Any ideas on what cause may be?

Start with plugs. Mine did the same last year.
Started and idled perfect, but bogged under a load.
It could be lots of things, but I always start with the the easiest and cheapest fixes first.
O'reilly's had my correct NGK plugs in stock.

I am asking for a friend. He said he put new plugs in already and still doing same thing.

Trigger, stator, switchbox, flooding injector if efi, stuck float if carb. That's where I would start.

I bet its the Stator.. Had it happen to me on two boats .....

Before you start buying electrical parts take the carbs off, take the jets out and clean it up. Pretty sure the high speed jets are plugged.

Stator. Replace it with a CDI stator and you'll be good to go. Mercury stators are notorious for going bad.

Mine blew up in Smith Lake this summer. 3 holes in the base of the motor.

Mercury replaced it, but took a couple of months.

Woowee stators are not cheap. This boat sat up for 2 years. Would water in the gas cause an issue like this. He also said at one point when he opened it up full throttle it bogged and cut off. If stator is bad, any danger of causing damage if boat needed to be run to get it out of water?

I don't mind CDI's switchboxes, but I usually stay away from all their other electical stuff. Just haven't had a lot of luck with them. Their ECU's are awful.

If the boat sat for 2 years, it's probably a carb/injector issue...especially if it sat up with ethanol fuel in it. Also check the fuel lines if it has been run with ethanol fuel...it will break down the inner liner in older fuel hose.

Don't forget the primer bulb.

If the stator is causing the issue it won't hurt anything to run it. If it is the stator causing the problem, it hasn't gone out yet, it's just going bad. It will eventually go out and when it does, that's the end of it. If you're on the water when it happens you'd better have a tow rope. As has already been stated l, I'd rule out fuel issues first since it's been sitting. Something as simple as a fuel tank not venting properly can cause the issues you described.

Their stators are 10x better than a Mercury stator.

I just haven't had good luck with them. I rebuild outboards on the side, and will go OEM every time on stators, triggers, regulators, and ECU's. Seen lots of CDI stuff fail.

I forgot to add. It just started this problem. He said it ran fine up until recently. If the carb was gummed up I would think it would have done it the first time on the water. We are going to pull the cover and see if can visually see anything.

Check the fuel lines and bulb first.

Took long enough for someone to bring this up.


Clean the carbs, dump the tank and maybe even change the fuel line depending on the age. Sitting idle is an outboar motors worst enemy.

I had the same problem with my old mercury and it's in the carb. He's gonna have to clean it and run clean fuel.

Ding, ding, ding! I'd say we have a winner with this answer. Same thing happened to me several years back. Ran perfect with the motor in a drum of water. Put it on the lake, put it under a load, and it'd bog down horribly. I hauled it back and forth to the shop that summer more than I hauled it to the lake. Finally, took it to a mechanic that put it in a big giant tub of water and strapped it down, where he could simulate being on the water. Ended up being the carb like Big Jack said.