Force 120 problem

[Tator22]

Hey guys new to the forum, gotta issue that’s been driving me crazy trying to figure out, I gotta 1997 force 120 on a nitro 185, rebuilt carbs, new impeller kit, new fuel lines, new plugs, new boyesen reeds. The motor idles amazing and runs good until WOT. It can’t go over 4K and we found the enricher valve was stuck always on, to which it is now disconnected. Tried adjusting carbs, timing, checked all cylinders for spark, nothing will correct it. Throttle is adjusted correctly according to service manual. Now the crazy part, I took it to the lake a couple days ago after doing some prop work and it did exactly as it’s supposed to, good hole shot and motor was running 5300 WOT. But started to die and found a broken fuel line, repaired line and then wouldn’t go over 4K again. Changed fuel lines again and same story. Took it to the lake and wouldn’t go past 4K, all of a sudden the motor opened up at it 5300k and really started pulling. Started to die and figure out I ran outta fuel. Put fuel in it and same story again, 4K max. So why is it that when it starts to loose fuel it decides to run like it should? Once with the broken line, then with it actually running out, both times it runs amazing until it completely runs outta fuel. It’s like when there is just enough fuel in the filter to run it, it goes right, but when it has fuel coming into it can’t build power. Pulled plugs 1&2 are clean 3&4 are blackened like it’s extremely rich on thoes cylinders. Any help would be much appreciated!

 

[roscoe]

rebuild fuel pump.
Torn diaphram inside will leak fuel into crankcase and cause a rich/flooded condition.

 

[Tator22]

rebuild fuel pump.
Torn diaphram inside will leak fuel into crankcase and cause a rich/flooded condition.

Got a kit on the way be here tomorrow , took it apart yesterday and didn’t see a tear in the diaphragm but don’t wanna rule out a pin hole.

 

[puffitu]

As roscoe suggests; fuel related-check butterflies and carbs( floats, jets, needles) as well. Diaphragm/fuel pump would be my first stop. You got a filter before the carbs?? What year is your engine?

 

[Tator22]

As roscoe suggests; fuel related-check butterflies and carbs( floats, jets, needles) as well. Diaphragm/fuel pump would be my first stop. You got a filter before the carbs?? What year is your engine?

Yes got a large 3/8 Wix filter after the pump, and 1997.

 

[CaptnKingfisher]

I think you have intermittent spark or weak spark condition on cylinders 3 and/or 4. Plugs are black because one or both of those cylinders is/are not firing regularly. When they do fire, you get full RPMs again, then the coil or whatever is failing heats up and you lost those cylinders again, dropping back down to 4k rpms.

Couple ways you can verify this diagnosis. Probably the simplest is a cylinder drop test. First run your engine at idle, note rpms. Then shut it down. Pull the plug wire off cylinder 4, ground the wire to the block to prevent any sparks or damage (I use a test lead with alligator clips to do this). Start the engine (now running on three cylinders) and note the rpms. If the cylinder you have isolated is normally firing, you will notice the rpms are significantly less than your baseline. Shut down the engine, repeat for cylinder 3, then 2, then 1.

If at any point, with spark plug wire off you are running at the same rpm as your baseline then you have found the cylinder that is not getting good spark.

The other way to find your issue is to test individual components in the ignition circuit according to your manual. And this will be your next step if a cylinder fails the drop test. And if your outboard passes the drop test I'll take my loss and help you chase the fuel issue lol

 

[Tator22]

I think you have intermittent spark or weak spark condition on cylinders 3 and/or 4. Plugs are black because one or both of those cylinders is/are not firing regularly. When they do fire, you get full RPMs again, then the coil or whatever is failing heats up and you lost those cylinders again, dropping back down to 4k rpms.

Couple ways you can verify this diagnosis. Probably the simplest is a cylinder drop test. First run your engine at idle, note rpms. Then shut it down. Pull the plug wire off cylinder 4, ground the wire to the block to prevent any sparks or damage (I use a test lead with alligator clips to do this). Start the engine (now running on three cylinders) and note the rpms. If the cylinder you have isolated is normally firing, you will notice the rpms are significantly less than your baseline. Shut down the engine, repeat for cylinder 3, then 2, then 1.

If at any point, with spark plug wire off you are running at the same rpm as your baseline then you have found the cylinder that is not getting good spark.

The other way to find your issue is to test individual components in the ignition circuit according to your manual. And this will be your next step if a cylinder fails the drop test. And if your outboard passes the drop test I'll take my loss and help you chase the fuel issue lol

I tested this sorta already lol Thought the same thing at first, checked the stator and had 3000 ohms between the 2 wires, checked spark on each CDM/ Coil and all were giving a blue spark at 1/2 gap. Tried champ plugs, NGK, and Autolites, but no change, back to champ now. At idle, unplugging 3 or 4 (tried this on all cylinders) created a very rough idle condition, have not tested at WOT. Just outta curiosity wouldn’t a intimidate spark issue create a basically quick “jump or boost in power” every now again when running? I only get full power when it looses fuel one way or another.

 

[CaptnKingfisher]

wouldn’t a intimidate spark issue create a basically quick “jump or boost in power” every now again when running?

Yes I thought that's what you were describing, problem seems to go away and reappear suddenly. But after reading about the results of your drop test and spark test I agree it's not ignition circuit related. The fact that you have two plugs blackened and the other two normal leads me to believe carburetor needs a rebuild (again) or youve got a blown head gasket. Or what Roscoe said, I wasn't aware a bad fuel pump could leak fuel into crankcase but definitely would be an easy thing to check out / replace if needed

 

[Tator22]

So pump is now rebuilt and so is carb( again) but fuel shoots straight out the 90 degree fitting going into the cylinder, flooding the engine to the point of leaking out off the foot and the carbs. Every time you hit the primer it shoot straight out of it. Suggestions?

 

[jerryjerry05]

(but fuel shoots straight out the 90 degree fitting going into the cylinder, flooding the engine to the point of leaking out off the foot and the carbs. Every time you hit the primer it shoot straight out of it.)
Pics of the 90d fitting? You shouldn't be able to see any fuel when you activate the primer.????

 

[oldboat1]

Measure spark on each lead with an open air, adjustable tester. Need about a half inch (7/16"?) In measuring spark, you are testing magneto strength.

 

[Tator22]

So figured I’d give an update for anyone in the future, the fuel pump issue was due to a faulty rebuild kit, new kit and no problem with fuel coming out the 90 fitting any longer. After a compression test found 148-151-150-152. Actually surprised it was so high for a 97 motor. But came to the conclusion it was a carb issue. Rebuilt the carbs (again) changed fuel lines, filter (again) and found during carb rebuild it had .094 jets in it. Seemed a little big to me so I went to the Mercury parts website and saw that .088 jets were recommended for my altitude (800ft). Fabricated some jets from a couple of brass screws. Drilled a 5/64 hole (roughly .078) and cut them down to the size of a jet. Boom, she ran perfect, gets the boat up to 40mph running 5100rpm with 4 people and fully loaded with tools and fishing gear. Had some actual .088 jets ordered and put them in and it smoothed out the idle even more and gave a better throttle response. Set timing to 30 degrees ( going for 28 degrees after I do some linkage adjustments) and had it on the water for 4 hrs yesterday without issue. Almost certain the jets were the cause of the problem. Not sure why it had that big of jets in it, especially in NC altitude. Thank you all for your help!

 

[Tator22]

So figured I’d give an update for anyone in the future, the fuel pump issue was due to a faulty rebuild kit, new kit and no problem with fuel coming out the 90 fitting any longer. After a compression test found 148-151-150-152. Actually surprised it was so high for a 97 motor. But came to the conclusion it was a carb issue. Rebuilt the carbs (again) changed fuel lines, filter (again) and found during carb rebuild it had .094 jets in it. Seemed a little big to me so I went to the Mercury parts website and saw that .088 jets were recommended for my altitude (800ft). Fabricated some jets from a couple of brass screws. Drilled a 5/64 hole (roughly .078) and cut them down to the size of a jet. Boom, she ran perfect, gets the boat up to 40mph running 5100rpm with 4 people and fully loaded with tools and fishing gear. Had some actual .088 jets ordered and put them in and it smoothed out the idle even more and gave a better throttle response. Set timing to 30 degrees ( going for 28 degrees after I do some linkage adjustments) and had it on the water for 4 hrs yesterday without issue. Almost certain the jets were the cause of the problem. Not sure why it had that big of jets in it, especially in NC altitude. Thank you all for your help!

Make sure if you rebuild one of these fuel pumps, you get a kit that doesn’t have the 2 hole in one of the diaphragms, that causes the fuel dumpage problem.