Out of ideas on Force 90, Help!

[JKEP44]

I'm no slouch at troubleshooting outboards but this one has me stumped. My dad recently picked up a 1990 Force 90 (model 908F90B) with what I believe is a Prestolite CDI ignition. The problem in the beginning was the engine would only reach around 4000 rpm at WOT and would on rare occasion (maybe once a day) have an issue where it would die transitioning from idle to full throttle. He ran it this way for about 5 outings. Now the engine will not get past transition at all and cuts out without so much as a sputter. The engine will reach full rpm out of the water on a set of muffs. Below is a list of what we have checked:
1. Cleaned carbs to operating room standards ensuring all air passages, jets and transition holes are clear. Also set float level and checked needle seats
2. Checked timing on a set of muffs.
3. Checked compression: 120,120,115 top
4. Pulled reed cages and looked for chipped/cracked reeds
5. Checked resistance on coils and plug wires
6. Checked stator output voltage
7. Disconnected rectifier
8. Ohm'd out ignition kill wire through throttle travel
9. Disconnected kill wire from engine
10. Ran complete new fuel source directly to filter screen.
11. Removed/inspected/cleaned filter screen
12. Plumbed in pressure gauge to carb fuel line (operates 5-10psi)
13. Checked fuel scavenge check valve and line from crank to intake.
14. Changed spark plugs
15. Ran borescope into top of cylinders and into bottom of Crank behind reed cage (nothing cracked or damaged)
16. Checked for plugged exhaust as best as possible, appears clear
17. Pulled plugs and turned engine by hand, turns freely feeling only resistance from impeller.
18. Adjusted carb to stator link as described in manual
I'm completely out of ideas at this point. I can't get a good look at the piston skirts but there is no sign of damage anywhere. The piston tops are black like its rich but I wouldn't think it would be so rich it wouldn't run. Any ideas anyone has would be great!

 

[recka81]

I had a similar problem on mine and it happened right after I put a new stator on. Wouldn't get past transition but was fine on muffs. Put old stator back on and it ran perfectly. Seemed like the brand new stator wasn't producing enough power. Was really weird.

 

[tommarvin]

It's an ignition part , it's going out now, or when old ignition part get hot/ overheat they have to cool down before they work correctly.
Remove the flywheel, look at the stator for brown or burned marks. Are the magnets tight.
Check every inch of wire on stator trigger cdi packs, coils, rectifier, especially where they go into connectors, give them a hard pull, are there any bare/broken loose wires.
outboardignition.com explains how to troubleshoot and test all ignition parts, wwwcdielectronics.com does the same but more complicated.
Your very good to know how to do all the things you have done so far, how do you plumb in a pressure gauge to carb fuel line we want to do that.

 

[flyingscott]

How did you check the timing on the muffs that needs to be done running in gear. Look at one of the stickies at the top about timing your motor from Frank Acampora. Have you done a cylinder drop test and have you tried pumping the primer ball while this was happening

 

[jerryjerry05]

What boat? Length?
​Load? Prop, size?

You have a DVA meter? It's needed to measure the stator output.
What stator? OEM or aftermarket.

Setting float level? How?
Setting drop? How?
​You have the regular choke or the primer?
The "new" fuel source? New lines and connectors?
Did the squeezie get hard when pumping it up?

5-10# of fuel pressure is about 7-8# more than required.
Operating range is 1-2.5 depending on the rpm.s
That could be the problem?????????

Timing??How did you do it running on muffs?

It sounds like the high speed windings aren't generating??

 

[ferdly1]

I had a similar problem on my 40 hp. It would run fine until I hit full throttle then it would die. I put a see thru fuel filter on and found the fuel line full of air. Found a loose fitting allowing it to such air. Also years before had same problem. I found a cocoon on the outlet valve of fuel tank. That liked to drive me nuts figuring out.

 

[JKEP44]

Hi guys, thanks for the replies.
1. Fuel pressure was plumbed in using a barbed T into the hose that goes to the carburetors off of the fuel pump.
2. I did squeeze the primer while running, no change.
3. Set flat level by the book, carb upside down leveled, float set to level.
4. New fuel source was a known good small tank from my aluminum boat set up higher than the normal tank of the boat with new fuel and fuel lines.
5.timing was set on the muffs (I know this isn't a great idea!) but with the boat in gear at full rpm..... Waits for angry replies....
6. Checked the stator, I have a DVA meter for work. We checked that back when it was actually making more RPM though so I might re-visit that.
7. I did look the stator wiring over and ohm' all the connectors, pulling on each one to make sure they are good. I haven't pulled the flywheel yet but that might be a good plan.
8. I haven't done a cylinder drop test and I don't know what that is, but I will go look at the sticky and figure that out. I did check to see if I was loosing a cylinder while running using the timing light and also a infrared gun.

 

[JKEP44]

I'm beginning to wonder if there is a conglomeration of ignition parts. I believe, based on the wiring diagram, this to be a Prestolite ignition. It has 2 CDI boxes, 3 coil packs, and all the components are blue.

 

[jerryjerry05]

The "blue" are the original packs and coils.
​Black came later.

The running at wot out of the water doesn't give a true reading.
I used to use a test wheel and that was in a tank in the water.

Cylinder drop test??? Just pull one plug lead at a time as you run the motor.
But if you got 4000 then that's probably not gonna show anything.

The 8-10# of fuel pressure might be overpowering the float and shutting it down???

Did the primer ball get hard when pumping?

At 4000 did it sound/feel like it was missing?

Any water on the plugs? the head gasket can leak and still have god compression.

Again, what kind of boat? Size?Load?
Prop, pitch, size?

 

[flyingscott]

YOU CANNOT time a motor in neutral revving the crap out of it needs to be under load to do it

 

[Jiggz]

You seemed to have done most of the troubleshootings except maybe for the following:
1. Validate the timing. First with the TDC marking the flywheel with #1 piston. This is to make sure the flywheel key is not sheared.
2. Install a clear fuel filter between the fuel pump outlet and the carb inlet. This will give you a visual on how the fuel delivery system performs on all engine rpm.
3. With the LU submerged in water, either at the lake or in a tub, ran the motor with the cowling cover off and inspect for exhaust leaks. If there is any indication of smoke inside the engine cowling you need to track it down where it is coming from. This can seriously affect engine performance while in the water but never if on muffs.
4. As for the blackened piston crowns, make sure the carb's fuel air mixture screws are set to one turn out from lightly seated or even up to 1 1/4 turn out.

 

[JKEP44]

Hi guys, sorry for the delay. I had to work a lot this week and just got back to the boat.
Info:
Boat is a Lund TYEE 4.9
It's heavy and loaded with a lot of fishing gear and batteries.
Prop pitch I'm not totally sure, it's a 15" aluminum
On to today's developments. You guys rock! All the talk about the stator made me pull the flywheel and look at it. It looks good with tightly connected ends and no brown spots, however!!!! I re-checked the resistance and found an anomaly. The way I see it there are three could on the stator. One for the rectifier, and two to generate spark. Wires #3 and 4 have the appropriate resistance of 735 ohms and are open to the metal ring of the stator. Wires #1 and 2 are extremely high resistance of 105K ohms and show resistance to the stator ring. I believe this is a problem if I'm understanding the system correctly??? This is different from when I originally checked it so I'm pretty sure it finally just failed.

 

[JKEP44]

No Title

On the trigger there are 4 pickups, 2 covered by black insulation and 2 shiny metal ones that have some scratches. A this still good? Is there a resistance check for this?

 

[JKEP44]

No Title

There isn't supposed to be any type of insert into the flywheel is it?

 

[pnwboat]

You have a bad stator. 105K means that the stator windings for #1 and #2 cylinders is not functioning. You're not running on all cylinders.