Thread: 87 merc 115 problems

Possibly needs fuel pump rebuilt. Check fuel line from tank to make sure it is not clogged.

i have already replaced the fuel line from the oiler to the engine.

First thing I would do is change plugs, then I would put a heavy dose of seafoam in the tank and run it hard for awhile. Give it a chance to clean any build up out of carbs. If possible and you have a lake close by, I like to back in water and leave boat on trailer. Crank it up and put in gear, run it about half throttle for about 15 minutes and see if it dosnt start to clear up.

I ran two cans of sea foam though it last summer still doing the same thing

Originally Posted by Kingz7

I have a 87 mercury 115 it start and idles great but when I get it out the water and plane out it cutting out and missing any ideas or some place I can start to look for the problem. Thanks

Replace ALL fuel lines from tank to carb, if that doesn’t clean it up, with the other things you have done... it’s time for a mechanic.


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I was having same problem as you Kingz7. I rebuilt fuel pump, replaced primer bulb & hose from fuel tank, and replaced the spark plugs. One of these fixed my problem. Runs like a scalded dog now.

Originally Posted by Kingz7

I ran two cans of sea foam though it last summer still doing the same thing

Change plugs

I have a 99 model 125 merc it was cutting in and out after plain and most times after a short run or long run when you started to backing out of it . it would shut off and it continued to get worse . had to change the big gasket( I guess head gasket) ? had water getting onto the plugs and was causing a misfire ! Been about a year since fixed and runs great ! Mechanic said that was the first one he had ever seen do that!