1998 Force 120 Stalls out in Low Gear

[L3af]

Does the primer bulb collapse when it is running? It shouldn't.
Fuel pickup in the permanent tank could be partially obstructed.

It doesn't collapse no, but the primer bulbs on both tanks seem to be hard and really hard to squeeze.

Whats the best way to find out if the pickup is clogged? disconnect it?

 

[topgun3690]

Whats the best way to find out if the pickup is clogged? disconnect it?

Do you have access to the top of your fuel tank? The fitting the fuel hose connects to.....it usually screws out and the tube comes out with the fitting.

 

[L3af]

Do you have access to the top of your fuel tank? The fitting the fuel hose connects to.....it usually screws out and the tube comes out with the fitting.

I do yes!

I'll check that after the vent!

 

[jerryjerry05]

Mercury uses a 5/16" hose and older Force used 1/4"
If your going to pull the pickup?? Be very CAREFUL as those fittings aren't meant to come out easily and can be damaged.
The best way to check the pickup is to empty the tank and then remove the sending unit and then you can see inside the tank. Snake camera 10$ ebay.
The vent hose: undo it from the top of the tank and then blow through it and see if there's an obstruction??? Bugs like to get into it if it's an open hose type. Look at the vent on the outside of the boat: is there any way that anything can crawl up in there?

 

[L3af]

I think I found the problem.

Finally got around to pulling the fuel/water separator. It was changed last year so it shouldnt be too bad. It was.

It was legit full of water, there was a "skim" of fuel on the top. I'm guessing this is most definitely the problem.



Now I gotta debate if I pump the tank out or not (it's full to the brim).

The Fuel Sender was put on wonky by the previous owner and water could have been getting in there. I fixed it last week, I thought that might have been the issues (maybe causing an air leak). But it might have just let in some water.

Fram G2 Filters should be here on Thursday.

I'll give the motor a run with the new fuel/water separator tonight and see if that fixes it.

 

[topgun3690]

Yep. That could be a problrm for sure.

 

[L3af]

Yep. That could be a problrm for sure.

That was definitely the issue.

Ran it WOT tonight for 5-10 mins and it's never ran better (which is kind of weird cause I put this water separator on last august and it didn't run this good).

It will be interesting to see how long the new filter takes to fill up, if theres a lot of water in the tank it wont take long. If that's the case I'll have to pump it out and clean the fuel.

Topgun, do you know which prop is best for the 1998 120 Force? WOT I only seem to hit 4000 RPM @ 32 MPH. It's a 1720 Key West, so I think it should hit 37-38MPH when WOT.

 

[Nordin]

That is the culprit or one of it.
Regarding the prop what size do you have right now?
4000 RPM at WOT is about 800-1200 RPM low
Going down 1 in in pitch would rise the RPM about 200.

 

[L3af]

That is the culprit or one of it.
Regarding the prop what size do you have right now?
4000 RPM at WOT is about 800-1200 RPM low
Going down 1 in in pitch would rise the RPM about 200.

It's a 3 blade but like you said its still tracking 800-1200 below what WOT should be.

I'll take off the carb covers and check the butterflies tomorrow.

What else could it be? Cylinder not working?

This has been the case since I bought the boat, so the compression numbers in the original post would apply.

 

[racerone]

Post compression numbers tested today.----Not 6 months ago.-----And does spark jump a gap of 3/8" on each lead.----Sounds like it is running on 3 of 4 cylinders.-----Changing the prop to get 1000 RPM more is the wrong approach.

 

[jerryjerry05]

yuky"s!!! now the fun starts.
Remove the sender, raise the nose of the boat as fare as it will go,
run a hose to the bottom edge of the tank.
Then siphon all the nasty's out. Checking periodically to see if you get the bad stuff and when the good gas flows add dry gas 5-6 cans. Then use a water sep that you can see the gas and try to keep it clean.
With that much water the fuel sender will probably fail so get ready yo replace it AFTER it's all cleaned up.

 

[L3af]

Post compression numbers tested today.----Not 6 months ago.-----And does spark jump a gap of 3/8" on each lead.----Sounds like it is running on 3 of 4 cylinders.-----Changing the prop to get 1000 RPM more is the wrong approach.

I'll have to wait till the boat is out for the summer to do that. It's in the water right now.

My point was that the boat has always had this as a top speed even tho the compression numbers were good.

 

[racerone]

You should be able to do a spark test in the water.-----Test run with a timing light one cylinder at a time.------Observe spark behavior.----Use a strong flashlight and shine into carburetor bore at full throttle.----Observe behavior of fuel coming up the main nozzles.

 

[L3af]

You should be able to do a spark test in the water.-----Test run with a timing light one cylinder at a time.------Observe spark behavior.----Use a strong flashlight and shine into carburetor bore at full throttle.----Observe behavior of fuel coming up the main nozzles.

Any videos on how to do this? The timing stuff always sounded confusing to me.

Post compression numbers tested today.----Not 6 months ago.-----And does spark jump a gap of 3/8" on each lead.----Sounds like it is running on 3 of 4 cylinders.-----Changing the prop to get 1000 RPM more is the wrong approach.

This is my first outboard so I'm new to some of these things.

Is this what you want me to do?

I have one of these, would that work? or do I need the tool that sets the gap? and is this it?

 

[topgun3690]

The tester you have will show if there is spark or not, but not how strong....use it to see if spark on all cylinders. The ones with adjustable gap will show how strong the spark is.....like being able to jump a 3/8 inch gap. I use one like this...

 

[L3af]

The tester you have will show if there is spark or not, but not how strong....use it to see if spark on all cylinders. The ones with adjustable gap will show how strong the spark is.....like being able to jump a 3/8 inch gap. I use one like this...View attachment 387032

Is this the same as that?

Does anyone recommend spark plug pliers when pulling the plugs while the engine is running to see which cylinder isn't firing?

Inexperienced and don't want to shock myself.

Other questions:

-I'm gonna be doing the impeller as I haven't done it yet. Should I do the water pump as well? Motor pee's great.
-Should I use genuine Mercury Parts?

Sorry about the delayed response, season is basically over here so I'll be pulling the boat within the week and get to work on all this.

 

[topgun3690]

Is this the same as that?

Does anyone recommend spark plug pliers when pulling the plugs while the engine is running to see which cylinder isn't firing?

Inexperienced and don't want to shock myself.

Other questions:

-I'm gonna be doing the impeller as I haven't done it yet. Should I do the water pump as well? Motor pee's great.
-Should I use genuine Mercury Parts?

Sorry about the delayed response, season is basically over here so I'll be pulling the boat within the week and get to work on all this.

That tester is about the same as the one I showed. The plug pliers would be a good idea.....keep you from shocking the #$%& out of you. The impeller is the heart of the water pump, if the housing looks in good shape(no pitting or deep gouges) it can be reused. If in doubt I would replace both. Cant go wrong with OEM parts but some aftermarket like Sierra are pretty good. You can get a pump kit that has the impeller, housing, plate and gaskets......