1996 Force 120 has trouble starting

[erikpn]

Re: 1996 Force 120 has trouble starting

as a complete neebie here.. can you define what a "lean Mixture" is exaclty? too much air in mixing w/ gas? or the other way around?

also just to confirm the screws that you are referring to are parts 23+24 on the following site::

http://www.dougrussell.com/partscatalog/components/index.cfm?fuseaction=viewparts&colid=06&coldesc=120%20H%2EP%2E%20%281996%29&index=2009&block=6&BlockNumberList=10,6,1,0,13,11,12,17,14,25,8,19,21,20,22,18,2,3,28,23,24,7,5,4,15,26,27,9,16

Yes. Not enough fuel with the gas. My plugs actually carbon foul badly at 1 turn out on the idle mixture screw, I start at one turn out and move it in to find the right setting according to the manual. If you don't have a manual, read the engine FAQs section of this forum and learn about what to do before you do it. Running lean for too long will melt your outboard.

23 is the idle MIXTURE screw. 24 is a spring, it is not a screw.

Idle speed screw is elsewhere on your motor,

 

[john from md]

Re: 1996 Force 120 has trouble starting

The carbs used on Force engines use the idle circuit as part of the mid range and high speed circuit also. If you make the idle too lean (less fuel), then you will have a lean mixture at Wide Open Trottle (WOT) as well. This is not good as the timing at idle is 0-2* BTDC and the timing at WOT is 30-32* BTDC.

Lean mixtures at WOT cause bad things to happen such as melted pistons.

John

 

[michaeljoffe]

Re: 1996 Force 120 has trouble starting

ok. i have a seloc manual.
when i actually start the process. should i have the screw set all the way in as a starting point, or just adjust to the less than 1 turn when the engine runs?
thx!

 

[john from md]

Re: 1996 Force 120 has trouble starting

First, if you haven't done so, do the basic carb/timing adjustment. That will set up your base line. Then set your mixture screws at 11/4 out. This will get you running, then throw it in gear and adjust the mixture and the idle and you will be set to go.

John

 

[michaeljoffe]

Re: 1996 Force 120 has trouble starting

John,

I'll reset the screw setting back to the manual spec.

Couple of questions:

• how can you tell if the mix is too lean/rich? engine stutter= too lean?
  
• what gets baselined first: timing or idle?
• Never having done either: What can go wrong ?
• i saw the defintion of BTDC, but what does that actually mean?

 

[john from md]

Re: 1996 Force 120 has trouble starting

Set your carb linkage first starting with aligning the trottle plate linkage with the control cable disconnected. All the procedures are in the book. Syncronizing the timing with the throttle will come afterwards.

Setting the idle and mixture is the last thing you do when you are in the water tied to the dock. It is set with the power lever in forward just out of the idle detent. You set it to 700-750 and then adjust the mixture looking for the highest rpm as you turn the screws. Again, the manual explains it pretty well. After the mixture is set, you go back and reset the idle speed.

When the idle is too lean, the engine tends to spit and jerk. It is actually backfiring but you can't tell unless the intake box is removed. When the engine is too rich, it tends to roll up and down in rpm and smoke more.

What can go wrong, nothing if you follow the instructions.

BTDC = Before Top Dead Center. Top Dead Center is when the piston is at the top of its stroke. To get power out of the engine, you must advance the spark as the throttle plates are opening. On the Force engine, the spark advances from 0-2* BTDC at idle to 30-34* at Wide Open Trottle WOT.

Regards,

John

 

[michaeljoffe]

Re: 1996 Force 120 has trouble starting

k will do this weekend... thx

 

[michaeljoffe]

Re: 1996 Force 120 has trouble starting

only had time to tweak mixture.. need to buy a timing light.
thanks.

BTW, what is the ideal RPM/ tilt angle to optimize speed. I can't quite seem to get it right.

MJ

 

[john from md]

Re: 1996 Force 120 has trouble starting

If you have electric trim, you set the cruise rpm that you want and then trim the boat until it is properly on plane. If you trim too far nose down, it will bow stear and feel squirrely and if you trim too much nose up it will porpose up and down. It also will trim differently depending on the weight of the boat. If you have one person in it, it trims differently than if you have four.

John

 

[michaeljoffe]

Re: 1996 Force 120 has trouble starting

Hi all,

After a few relatively trouble free months, i had to get towed back to shore after getting skunked for salmon.
Starter would not crank.. Now am being told that the wire gauge from battery to starter was not thick enough. Getting that replaced and having the manufacturer check out the starter.

Im now having compression issues with one of the cylinders. It is firing at 50 psi instead of 120.

Is this a simple fix or am i looking at something complicated?

Thx

 

[john from md]

Re: 1996 Force 120 has trouble starting

Well, it could be stuck rings which can be cured by doing a couple of Decarb treatments. It can also be a head gasket.

Try the decarb and let it sit in the engine overnight if possible before trying to blow it out, then check compression after a hard run. If it didn't come up, it is probably a gasket. If it came up, say to 80, then give it another decarb.

 

[moparman]

Re: 1996 Force 120 has trouble starting

btdc means before top dead center=amount of degrees before the piston is at top dead center[piston all the way up in the cylinder bore] i.e. 32 degrees means the piston is 32 degrees before top dead center.

 

[olow]

Re: 1996 Force 120 has trouble starting

the btdc means before top dead center

 

[michaeljoffe]

Re: 1996 Force 120 has trouble starting

Still want to strangle the guys that installed the starter..arghh.

Decarb update:

Ran about 5 gallons through the engine, didnt have a chance to let the sea foam sit overnight ( inserting directly into cylinder?). The compression didnt really change, I will crank it agin in the am for sport...

Observations during decarb:
Heavy white smoke then it cleared up.
Noticed that every 10 sec or so, a thick puff of white would pop out...Backfire? Air mix not right im guessing..

Plugs:
ran test with all plugs out as well as removing 1 at a time.
1: 120 CLean
2: 50-80 Clean (comp issue)
3: 120 dirty
4: 120 very dirty, carbon caked on

Not sure what this (dirty plugs) means if anything. 50:1 gas mix

Gasket looks original and some flaking is present.
Is there a temp gasket fill until i get get a new one? Need the boat for a few more weekends

 

[john from md]

Re: 1996 Force 120 has trouble starting

First, what gasket are you talking about?

Next, the plug indications show that the engine is running lean from the top. This can be because of the low compression on the number 2 cylinder. This cylinder operates the fuel pump. If the decarb didn't fix the problem, then the next place to look is to see if the head gasket is damaged. Is this the gasket you are talking about?

If the head gasket is the one you are talking about, you can get it from any Mercruiser dealer. It will be more expensive than buying it from Iboats or ebay but you will have it faster.

 

[michaeljoffe]

Re: 1996 Force 120 has trouble starting

Thanks... yes i meant the head gasket.

I need to go find my manual...

• Are there any suprises when replacing this item?
• Will the seals (rings) on the piston work correctly once i change it or should i have a few just in case?

Also, does the fouling on the plugs incidate a bad air mixture in general?

thx!

 

[john from md]

Re: 1996 Force 120 has trouble starting

Replacing the head gasket is simple, just remember to torque the bolts in the order specified and clean the mating surfaces. Oh, don't use any grease or gasket sealer on the head gasket as they are actually detrimental to it sealing properly.

You can't access the piston rings from the head so you don't need spare rings. If the head gasket doesn't fix your compression problem, you will have to tear down the engine if you want to replace the rings.

As for your mixture, you need to get your compression fixed before making any mixture determination. This has to do with the design of the engine in how the fuel mixture circulates as well as the operation of the fuel pump.

While you have the head off, do a good inspection of the cylinder and see if it has any gauges that a broken ring would cause.

 

[michaeljoffe]

Re: 1996 Force 120 has trouble starting

Should I spray the pistons with seafoam or some sort of lubricant before putting everything back together?

 

[john from md]

Re: 1996 Force 120 has trouble starting

Unlike a four stroke engine, a two stroke engine supplies oil with the fuel. It is not necessary to use an assembly oil or such when assembling two strokes. I actually will cause more carbon and fouling as the oil to fuel ratio will be too high.

 

[michaeljoffe]

Re: 1996 Force 120 has trouble starting

what about seafoaming them?