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CarlWBL

Mercury outboard "bogged" down

10 posts in this topic

I have a 1993-1995 Mercury 20hp tiller on my Lund. Just recently I have been experiencing a "bogging" down problem. When I open it up, it will only go about 2-3 mphs, then after a little while (sometimes), the gas will shoot through it and the engine will lurch, then it will work fine. Any suggestions? My thoughts are that I may need new spark plugs or some c-foam in the carbs. Let me know if this is the right train of thought.

Thanks.

Carl

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Sounds to me like a probable carb issue. Running sea foam through could help, but you may require more than that.

The next time you're out, when it bogs hit the choke and see if it picks up. If it does it's a carb problem, a restriction in the high speed jet.

marine_man

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You may also have intermitant spark on 1 cylinder. The lurch you feel could be the dead cylinder fireing. If you have a timing light hook it to each cylinder and observe the light. Doing what MM suggests is also a very good way to determine if the problem is fuel related.

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I have a 99 150 EFI that does the same thing. Once it gets warmed up it seems to run fine. It doesn't do it all the time, only about every 3 trips or so. Have tried sea foam, spark plugs, filters, fresh gas and am about ready to take it in to be looked at. Would this be the same problem as Carls motor?

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One thing you might want to look at is having your carbs synched. My 99 40hp four stroke exhibited a low end bog especially on fast accelerations - had the carbs synched and no problems. Problem did not occur if I accelerated slowly. Once over the 2200 RPM "hump" it worked fine. Not sure if this is your problem - maybe just something else to check.

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When I was running my motor, I pulled the choke out and it seemed to bog down even more.

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I'd have to say you are not starving for fuel then. Either loading up (flooding) or an ignition problem. If it feels like you are flipping a switch, its ignition. A slower or gradual onset would indicate flooding.

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I agree with boatfixer. Sounds like your running on one lung then the sudden firing of the dead cylinder coming back.

I'd start with fresh gas and new spark plugs. I think you'll be fine after that. While you in there check the condition of the plug wires. Inspect the plugs and you'll probably notice a difference between the two. The black and or wet plug will tell you which cylinder isn't firing.

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Thanks everyone. I need the boat ready by this weekend for a trip up north, so I will post how it goes. I am going to try replacing the spark plugs first and hopefully that will be the solution.

Carl

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If that doesn't fix it, back the boat / trailer into the water. Run the motor at WOT, and if it bogs, pull a spark plug wire (make sure they're insulated or plastic pliers) and see if it kills the engine or stays the same.

The one that stays the same is the cylinder you're having issues on - check for spark, then it might be time to dive into the fuel system.

marine_man

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