120 Force Outboard by Mercury

by Wesley
(Houston, Texas)

So I just bought this boat from a buddy and it has a 1996 120 HP Force. The problem is to get it to idle while it is in the lake... It will idle all day long on the water hose but when you put it in the lake it will not stay idling.. I checked the reeds and the reeds are fine I took the carbs off and cleaned them they didn't look bad at all. I put in new plugs but I haven't had a chance to take it back to the lake since I have done those things, so any ideas if I get out there and it is still doing the same thing?? Any help or advice would be awesome..

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Jun 30, 2014
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idle in water vs. on hose
by: Anonymous

From my experience and what most manufactures say, idle adjustments should be done with the boat in the water under load ( in gear ). This will make it idle a bit higher on the hose in the yard where there's no back pressure. I did this on my 1990 Johnson 40 hp and it does help with stalling at idle. Also remember the ignition timing is the major contributing factor for idle speed. Don't just crank out the low idle screw alone ( if your model has one). Adjust the spark advance linkage as well. I would even adjust the spark advance linkage before I turn the idle screw at all.

Mar 16, 2014
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120 horse force won't idle in the water
by: Bruce

I had about the same problem with the 115 Evinrude. It would start fine and run all day on a flush in the driveway. But put it in the water it would not even start but if it did it would run.
When I bought the boat somebody had taken it apart and put some replace a piston and when they put it back together they did not use new gaskets. Initially I looked over the motor to see if I could see if anything was wrong by giving it the old Eagle eye. I found some silicone that was smeared over a gasket I figured sormebody had someone your finger and just wiped it off later the marina said there was a vacuum leak right there where I feel that silicone off. When I replaced that gasket motor ran perfect.
sounds like you have a vacuum leak.
It is easier for the motor to start out of the water because it only has to suck air but if you put the motor in the water it will have to suck water up out of the lake and air so it won't be able to suck enough gas to start the motor.
Yes my motor did start in the water when I was having trouble I would have to nearly wear the starter out to get it going but once it got going it would run but I guess that just depends on how big the vacuum leak is.

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