1995 90HP Force Outboard Fuel Starvation

[Jack.fz]

Hey, I've been lurking on this forum for a while and having difficulty solving my issues still.

Background:
Leaving John Pennekamp park in the Keys one weekend the motor stalled in full RPM's right out of the channel, messed with it for a while that day and noticed the choke solenoid / enricher valve was leaking. After choking the motor, got it to run for the rest of the weekend progressively choking it. After I got back home I let the boat sit for 2-3 weeks before its next use while I waited for the new solenoid to arrive. Once I tried to crank boat again it would run for just a couple seconds, back fire and fie. Then there was no spark (presumably but I did notice the spark tester wasn't operating), I then went through trouble testing spark issues, every test I did didn't seem to work out, I changed the ENTIRE ignition system. New Stator, CDI, Trigger, Voltage Regulator. Now the boat has spark again but a new issue, it will not accelerate under load. The numerous times I've tested this on the lake I've found the some times it will reach full RPM or near full RPM, it's very random and happens extremely infrequently and for unknown reason.

Fuel system testing;
Tank vent is clear, fuel filter seems to be working good was replaced in June 2020, tried running motor on portable tank bypassing filter with same results. I changed the fuel pump diaphragms, which I'm not sure if I did correctly but it seems to be doing the exact same thing and the old diaphragms only looking worn but no cracks or other issues. The carbs were cleaned twice and taken apart 3 times, jets, needles and floats all appear to be sitting correctly.

The stator is sitting slightly shifted towards 9PM on a clock as the fiberglass on the new one around the wires caused the trigger not to be able to move. I have checked and it seems as if the trigger is moving towards full advancement, I don't believe there to be a linkage or a timing issue.

Cold compression check:
Cyl. 1. - 95 PSI
Cyl. 2. - 115 PSI
Cyl. 3. - 110 PSI

I have no idea where to move forward from here, it has been consuming all my time and energy and I can't even go fishing lol.

 

[jerryjerry05]

First, check the primer for power after startup.
Sometimes the key switch keeps the primer
feeding the carb and if so it won't get to full rpms
and can even stall the motor.
Backfire: even 1 tiny backfire can blow the gaskets
on the port covers(3) this makes the motor suck air.
Do a starting fluid test: start motor, spray SF around
the intake side and behind the carbs and port covers.
If this makes a difference in the way it runs?? Then
fix the gasket.

 

[racerone]

Some will argue -----Those compression numbers indicate a problem , like a scored piston.-----Pull cylinder head to have a look.----You have installed a new impeller in water pump ?

 

[Jack.fz]

First, check the primer for power after startup.
Sometimes the key switch keeps the primer
feeding the carb and if so it won't get to full rpms
and can even stall the motor.
Backfire: even 1 tiny backfire can blow the gaskets
on the port covers(3) this makes the motor suck air.
Do a starting fluid test: start motor, spray SF around
the intake side and behind the carbs and port covers.
If this makes a difference in the way it runs?? Then
fix the gasket.

I will give it a try, in an attempt to find the problem I also removed the reed plate and checked all the reeds and replaced with new gaskets as well as new carb gaskets. I have several primer solenoids now and I will try testing a few of them on the water for any differences as well.

To clarify, it idles fine sometimes; occasionally it will halt at almost perfect times as if it missed a spark and do it several times before dying. But sometimes it will idle for 15 minutes plus without an issue.

It hasn't been backfiring since I changed the ignition system

 

[Jack.fz]

Some will argue -----Those compression numbers indicate a problem , like a scored piston.-----Pull cylinder head to have a look.----You have installed a new impeller in water pump ?

I went over compression with quite a few people so far, I thought it could be concerning the first cylinder has lower compression but the general consensus I received was that 95 cold should be OK. Also while on the water at full throttle it will sometimes grab RPMs and fully accelerate so I don't believe there is an issue internally as once at full RPMs it will continue to run smooth until throttled down.

I recently did the water pump impeller last week as the water flow had noticeably slowed down while I've been messing with it.

 

[racerone]

You could run with a timing light to observe spark as you increase throttle.-------I do know that a 20 PSI difference in a modern motor indicates a problem !!-------But in the big picture a head gasket is cheap.----Take the head off and have a look in there.

 

[The Force power]

As Racerone already mentioned; verify with a timing-light for proper ignition.
It is possible that the head gasket is blown/leaking and causing the the low reading
You mentioned that you changed the Stator did you set up the timing correctly?

If TDC occurs at the TDC mark and you can set the 28* WOT STATIC TIMING (plugs removed and wires shorted to ground). then the timing must be correct. If not you have a trigger problem,
It is also possible that the trigger magnets have shifted on the hub, but unlikely.
HERE'S A POST WRITTEN BY THE LATE FRANK A.
(follow this to the T do not skip any steps!!!)

1.Disconnect the ball link to the carb cam at the timing tower. Disconnecting at the cam risks bending the cam. Move the cam away from the carb roller.
2. Loosen the screw(s) on the aluminum tie bar and let all carbs close completely, then tighten again.
3. Set the cam so that the scribed line is pointing directly at the black roller on the carb lever. If the cam has two closely spaced lines, set the black roller directly between them.
4. The black roller is held with an offset screw and nut. Loosen the nut and turn the screw until the black roller JUST touches the cam. Tighten the nut and re-attach the ball link maintaining the scribed line at the roller.
5. Adjust the ball link so that at full throttle the bottom carb butterfly opens substantially horizontally. Adjust the aluminum tie bar so all carb butterflies open equally at full throttle. They need not be perfect but should be rather close to horizontal for best performance.
6. Adjust timing to 30 degrees before top dead center at full throttle.
7. Adjust idle speed to 700-750 RPM in the water in forward gear. Do this with the screw on the bottom of the timing tower. Loosen the locknut and adjust. Screwing in increases idle speed. Do this in small increments and let the engine rev and adjust itself before the next adjustment. A little goes a long way here. When correct, tighten the nut. Note that the scribed line on the roller will now be (usually) below the black roller a bit.
8. NOW we adjust the mixture on the carbs. Set all low speed needles to about 1 1/4 turns out from lightly seated. Do not force as this will damage either the needles or the seats.
8A. With the engine idling in neutral, turn each the needles in equally about 1/8 turn at a time. Give the engine a couple of seconds between each adjustment to stabilize. Adjust until the engine either "sags" or stalls. Note this setting.
8B. Now go the opposite direction. Adjust until the engine runs rough, burbles, or stalls. Note this setting.
8C. Set all needles to the average between the two settings: That is, for example, if it stalled at 3/4 turn out and burbled at 1 1/4 out then set all needles to 1 turn out.
8D. Readjust idle speed to 700-750 RPM.
9. Take the boat out on the water and do a "hole shot"--Full throttle acceleration from a stop. If the engine "sags" then recovers and picks-up it is too lean. Open the needles about 1/16 turn at a time until the engine accelerates with no hesitation.
If the engine sputters or coughs or burbles, then clears itself and accelerates, it is too rich. Close the needles about 1/16 turn at a time until the engine accelerates smoothly.


10. I can NOT stress this enough! NEVER set the low speed needles less that 1 turns out no matter how poor the idle or acceleration. To do so will run the engine too lean and detonation and melted pistons at or near full throttle operation will result.

 

[jerryjerry05]

If this is the Mercury ignition system??
Then the "trigger magnets" I don't think
are used???
Turn the flywheel over and take a picture.
When FrankA (RIP))made this post it was for the
pre Mercury setup.

 

[racerone]

How can a " lean setting " on low speed needles result in detonated pistons at full throttle ??

 

[topgun3690]

"10. I can NOT stress this enough! NEVER set the low speed needles less that 1 turns out no matter how poor the idle or acceleration. To do so will run the engine too lean and detonation and melted pistons at or near full throttle operation will result." This statement has led to several spirited debates here in the past, IIRC.....

 

[racerone]

Does any fuel come out the low speed jets at full throttle ?-----This lean " low speed setting " and the way those carburetors work is not well understood I think.

 

[pnwboat]

Yes, the idle speed passages do supply fuel at higher RPM's. The difference between idle and higher RPM's is the position of the throttle plates, and where the idle/low speed mixture ports are drilled into the side of the throttle bore. From idle to about 1/8th open, just the idle/ low speed ports are exposed to engine vacuum, and not the main fuel supply port. This causes the fuel to be sucked into the motor via the idle/low speed ports. Once you open the throttle plates more, the main fuel supply port is exposed to more engine vacuum, and the fuel begins to flow through it and the main jet. Pretty simple but this is how they did it back then.

If you look into the throat of the carburetor, you'll see a small brass tube that goes from the bottom to the top. This is the fuel supply tube for the idle/low speed passages. If you look at the upper/top area ofthe carburetor throat, towards the base/back, you'll see a couple of very small holes (depends on what model carb as to the number of holes). These are the idle/low speed fuel supply. You have to open the throttle plates to see these as they are not visible with the throttle plates closed.

The hole that the small brass tube comes through is actually the fuel supply from the main jet.

 

[Jack.fz]

I really appreciate everyone's responses.
Going forward I think the timing would be the most likely cause to these issues, I'm going to verify timing is set up properly before proceeding.
Head gasket is not blown btw.

I recently purchased a new(er) motor and plan on using a jack plate so I'll be able to swap back and forth to test the Force motor out after properly setting the timing up.

Again I really appreciate everyone's responses.

 

[jerryjerry05]

Early in the post you said "Also while on the water at full throttle it will sometimes grab RPMs and fully accelerate so I don't believe there is an issue internally as once at full RPMs it will continue to run smooth until throttled down"
This leads me to believe the ignition system has a problem.
A loose wire or bad connection or a pinched wire??

 

[The Force power]

Yes, the idle speed passages do supply fuel at higher RPM's. The difference between idle and higher RPM's is the position of the throttle plates, and where the idle/low speed mixture ports are drilled into the side of the throttle bore. From idle to about 1/8th open, just the idle/ low speed ports are exposed to engine vacuum, and not the main fuel supply port. This causes the fuel to be sucked into the motor via the idle/low speed ports. Once you open the throttle plates more, the main fuel supply port is exposed to more engine vacuum, and the fuel begins to flow through it and the main jet. Pretty simple but this is how they did it back then.

If you look into the throat of the carburetor, you'll see a small brass tube that goes from the bottom to the top. This is the fuel supply tube for the idle/low speed passages. If you look at the upper/top area ofthe carburetor throat, towards the base/back, you'll see a couple of very small holes (depends on what model carb as to the number of holes). These are the idle/low speed fuel supply. You have to open the throttle plates to see these as they are not visible with the throttle plates closed.

The hole that the small brass tube comes through is actually the fuel supply from the main jet.

Thank you for this detailed explanation so I & many others actually learn the fine intricate details on how it evolves

 

[The Force power]

If this is the Mercury ignition system??
Then the "trigger magnets" I don't think
are used???
Turn the flywheel over and take a picture.
When FrankA (RIP))made this post it was for the
pre Mercury setup.

These are frank's words (incl. about the trigger-magnets)
Jack.fs says he has a '95 so it would be with a Merc. ignition.

 

[Nordin]

Thank you pnwboat for the eminent explanation about the air/fuel idle speed settings impact at higher RPM and WOT.
There are many folks that has questioned me about this theory and I have not been able to explain it.
I asked Frank A about this a long time ago in this forum but he did not have time to explain it to me that time.
I took his word for it from the FAQ topics cause he was a Chrysler/Force pro.

 

[Jack.fz]

This leads me to believe the ignition system has a problem.
A loose wire or bad connection or a pinched wire??

I triple checked wiring as I replaced everything regarding ignition besides coil packs and wires themselves as I tested them and they seemed to be functioning. Maybe I'll bring the DVA back out and test trigger and CDI.