1999 mercury force 120 hp help

[Falroy]

Hi all I have been searching through old threads to help me come up with a solution for the issue I am having with my motor. So last year at the beginning of the season I took by boat out for the first time and it ran fine then I docked it for a few hours again and tried to fire it up and the engine was suddenly running really rough and had almost no power. After that it was hard to get started and would barely idle if at all and will not go into gear without stalling completely. I have changed the spark plugs and replaced some of the seized check valves on the fuel re-circ system. I am going to get a compression gauge to check all of the cylinders and I have also bought the clymers manual. I have a little experience with working on small engines and such and do all my own maintence. Any advice at all no matter how basic would be greatly appreciated.

Thanks in advance

Chris

 

[Mi duckdown]

Re: 1999 mercury force 120 hp help

Compression is always a good idea. Number one on My list to check.

 

[Falroy]

Re: 1999 mercury force 120 hp help

I have finally been able to test the compression and all cylinders are within 135 psi and 142 psi. I am not sure what to check next. Like I said in the original post the engine was running really rough almost like it was miss firing. All cylinders has spark as well. The exhaust also seemed a little smoky????

 

[Falroy]

Re: 1999 mercury force 120 hp help

If anyone has any ideas I could really use the help

Thanks

 

[oldman570]

Re: 1999 mercury force 120 hp help

Compression is good, good spark, all that is left is the fuel system. Ether the carbs are in need of work or there is a air leak or obstruction in the fuel system. If using gas/ethanol fuel check the fuel hoses for blockage and bad lining. Ethenol has a tendency to eat up old rubber style fuel hose. JMO
Oldman570

 

[Falroy]

Re: 1999 mercury force 120 hp help

Thanks oldman570 I will definately check those things and post an update.

 

[Falroy]

Re: 1999 mercury force 120 hp help

So my problem definatly is delivery of fuel from the tank to the carbs. Fuel seems to
Be comeing out of the front of the lower carb when the engine is running and you can see a slick of gas on the water when the engine is running. The thing that gets me is it was the first time out for the season and when I first fired up the motor it ran fine then when I started it up again after a couple of hours the problem started. Just make me think something is gummed up are some partical has come loose and plugged something or effected the float. It really does feel like the motor is running to rich. I am definatly no expert on carbs so any help figuring this out would be great.

 

[Mi duckdown]

Re: 1999 mercury force 120 hp help

Things go bad when you least expect. Maybe a bad float or needle stuck.?

 

[roscoe]

Re: 1999 mercury force 120 hp help

Running like it is flooded ?

Probably is.

Fuel pump leaking gas directly binto crankcase from a torn diaphragm.

Pop the fuel pump open and look for pin holes or tears.

Then put in a rebuild kit, $20 from Merc dealer.


Then check the enrichment valve, Merc's version of a choke.
When you push the key in to choke, the valve opens and dumps fuel into the manifold behind the carbs.
It may be stuck open.
Pinch off the fuel hose feeding the solenoid valve and see if the problem goes away.

 

[Falroy]

Re: 1999 mercury force 120 hp help

Ah Rosco thanks for the advice

It definatly seems like it is the bottom carb as fuel dribbles out of it when trying to start the engine. I shut off the valve going from the fuel tank to the pump and after a few cranks the engine ran fine until it died from a lack of fuel. I will check the diaphragm in the fuel pump. I pumped the primer when inhale the carbs off and could hear air pumping from the where the lower carb mounts. Thanks a lot for the advice

 

[Falroy]

Re: 1999 mercury force 120 hp help

I also checked the float and needle and as far as I could tell they both seemed fine

 

[Falroy]

Re: 1999 mercury force 120 hp help

Thanks everyone for all of your help. I checked the fuel pump this morning and one of the diaphragms was almost torn in half. I went and picked up the rebuild kit installed it and the motor now runs better than it ever has. In total i replaced the apart plugs cleaned the carbs and changed out three faulty check valves in the fuel re-circ system. Thanks again for all the help!