1996 Force 120 hp Rough Idle and Part Question

[gprocks]

I need help with a this one. We put 4 new plugs in and it ran like it has never run before, very smooth, lots of power. Then shortly after refuelling with 50:1 mix, the motor started running really rough at idle. It doesnt also perform as it should - maybe 5-6 MPH slower at WOT (5200rpm) than it should.

I suspected it was water in the fuel so I added Fuel treatment and stabilizer then sprayed Mercury Power tune through both carbs. It seemed to help but still is really rough idle and stalls once in a while when shifting into gear. Also the motor shakes when rough idling. It seems louder than it usually is too (this could just be my imagination though). Also there are 3 small holes side by side at the back of the motor (prop side) just under the powerhead cover. These sit at or just above the waterline on the leg of the motor. I never noticed any action out these holes before (they could have though - we recently got the boat so didnt pay attention to this). Now there is air blowing out these holes/spurting as it idles - it could be exhaust. What are these holes for - is this normal?

I am thinking now it could be one of the new plugs is faulty? anything else I should check or replace (fuel filter, etc.) - let me know what you think.

GP

 

[199675hpforce]

Re: 1996 Force 120 hp Rough Idle and Part Question

I just played around with mine today on muffs. I have the clymer manual but doesnt mention how to adj idle. Ive gone through the entire manual reading but alot of times they included certain models and exclude others confusing and time consuming. There was a big stainless steel screw with nut attached i spun down a little. The line on butterfly that opens wasnt perfectly centered maybe i will take shift control linkage and spin that out a few turns to line up line with center screw. Mine runs better now, i ordered a new fuel pump kit but not sure i need it.

 

[199675hpforce]

Re: 1996 Force 120 hp Rough Idle and Part Question

I just played around with mine today on muffs. I have the clymer manual but doesnt mention how to adj idle. Ive gone through the entire manual reading but alot of times they included certain models and exclude others confusing and time consuming. There was a big stainless steel screw with nut attached i spun down a little. The line on butterfly that opens wasnt perfectly centered maybe i will take shift control linkage and spin that out a few turns to line up line with center screw. Mine runs better now, i ordered a new fuel pump kit but not sure i need it. Ive got my carb screw out around 3/4 turn maybe 1 turn out, oil was dripping out the bottom maybe i can lean this setting out little bit.

 

[roscoe]

Re: 1996 Force 120 hp Rough Idle and Part Question

Check your plugs, what do they look like? all the same?

If it is water in the gas, it will continue untill you get all the bad fuel out of the tank.

 

[6boats]

Re: 1996 Force 120 hp Rough Idle and Part Question

Been there.
Check fuel first. Remove fuel pump and check diaphram, and valves. All 3 valves must work. Clean vacuum lines and hoses with clean air or computer cleaner. Replace the hose just after the fuel pump and replace with a long 4 ft hose and place the open end of the hose in a glass jar away from the engine. On a COLD engine only, crank the engine just long enough to check gas flow. WARNING: use a long hose, glass jar, and don't pump gas on the engine. WARNING: You could start a fire, so keep a fire extingusher handy.

Fuel OK? Reconnect all fuel lines and clean up any fuel spills.

Check electrical. Remove ALL spark plug wires and test for spark. Use a good set of rubber gloves and place a Phillips screwdriver in one of the spark plug wire connectors. Crank the engine just long enough to see if the Phillips screwdriver makes a spark against the spark plug.

If you have an electrical problem, FIRST make a complete electrical diagram with wires, parts, colors, wires grounded, and wires at 12V.

With a good electrical diagram, start swapping parts. Swap spark plugs first. Retest. If all Spark plugs are good, swap Coils, and retest. If all coils are good, swap Power packs. If all power packs are good, you can try swapping stator wires or trigger wires. Sometimes you cannot tell if the stator or trigger is bad, unless you remove the parts and measure them electrically.

 

[gprocks]

Re: 1996 Force 120 hp Rough Idle and Part Question

Thanks Roscoe & 6 Boats,

I ran the old fuel out and put 10Gallons of fresh gas in. Also replaced the new plugs - the old ones looked really clean - one had a bit of black on it (2nd cyl from bottom of block), but certainly not enough to effect performance - These are the BUHW plugs (no gap, just flat strike on bottom).

It seems to run better, not nearly as rough on idle - stays running but not like it usually does. I'll ride out this gas and see if it still is running funny on the next fillup and then get into the fuel system if I have to. I think the next step is I will replace the fuel filter just in case it's holding water.

Thanks so much for your help. Any idea what the port with the 3 holes on the back of the motor is? Is it just an exhaust port?

GP

 

[6boats]

Re: 1996 Force 120 hp Rough Idle and Part Question

sounds like the impeller pump visual outlet. water should come out of there when the engine is running.

 

[kandil]

Re: 1996 Force 120 hp Rough Idle and Part Question

This holes are for the exhaust you have a dull exhaust out from the snout above the prop and from this hole

 

[hedoking]

Re: 1996 Force 120 hp Rough Idle and Part Question

hey 6,im having kinda the same issue with my 35 hp force. itll start,though its hard to get started,run rough,cough a few times,each time it seems to try and pick speed back up but will eventually die a few seconds later.this is my first outboard soforgive me for saying so but im kind of a dummy in this area. i checked and changed the plugs(still have the problem) cleaned the carb...found gum in the bottom of the bowl.fuel filter is clean,has new fuel in the tank,mixed 50 to 1. this motor was stored for the better part of 10 years prior to me getting it. please help. any suggestions or knowlege would be greatly appreciated.