1994 merc 115 outboard stumbling on acceleration

[fireguyfire]

Hi fellas; I am having one more fairly minor issue with my otherwise sweet running motor. When rapidly accelerating from idle (like when trying to launch a skier or wakeboarder) the motor has a tendency to stumble, and sometimes stall. If I fairly slowly and steadily accelerate it works great. Any ideas what my problem is, and how can I fix it?

 

[enginepower]

Is that a carb or efi motor? Could be low float level on carb. Bad spark plugs or weak spark. Lean carb at idle can cause hesitation on rapid take off. Probably need to do a compression test as well.

 

[gbrowne9]

check the accelerator pump on the bottom of the throttle cam. it has 2 little hoses that go to the bottom 2 cylinders.it,s like a fuel pump diaphram.

 

[gbrowne9]

check the accelerator pump on the bottom of the throttle cam. it has 2 little hoses that go to the bottom 2 cylinders.it,s like a fuel pump gasket

 

[fireguyfire]

gbrowne9; what am I checking for?
enginepower; it is a carb motor and the plugs are brand new and the spark is strong.

 

[Nathan Bond]

All things being equal (good gas, strong spark, timing set correctly), it's probably as engine power suggested, either carbs running on the lean side or low float level. If your carbs are running lean, it's a simple adjustment of the idle screw. Or, you could have a little dirt in the carbs partially blocking idle fuel flow.

 

[racerone]

That motor may be a 2+2 design.--Only gets fuel for idle on the top 2 cylinders.----Bottom 2 carburetors kick in at around 1800 RPM.------Going to run rough on transition.-----But check if acceleration pump diaphragm is working properly.

 

[fireguyfire]

Thanks for the tips fellas, I appreciate it. Gonna ask one more question as I am a car guy, not a boat mechanic;
How can I check if the acceleration pump diaphragm is working properly? Can someone give a shadetree boat wrencher a basic description of where it is and how to test it? Cheers!

 

[enginepower]

Well car guy, you must be young lol. Old school car carbs have accelerator pumps. Just make sure carb is full of fuel by pumping primer bulb and open the throttle and see if fuel is squirting out (you will have to remove air intake cover to see this if your carb has an accelerator pump)

 

[Nathan Bond]

My merc 115 (2005) doesn't have accelerator pumps, just standard fuel pump and enrichment valve for starting. If it's a 1994, it's probably due for a carb cleaning/rebuild.