1995 Force 90 - runs poorly at speed

[Bannister 6905]

Looking for anyone who's had a similar issue with their Force 90...

The motor starts well and idles fine. However, when coming up on plane, it stutters, vibrates and is reluctant to rev. Eventually, it will plane out, but it struggles. Top speed is about 2/3s what it should be (1995 17' Pro Line CC). 17" pitch aluminum prop. When the motor starts to struggle, I pump the primer bulb, which is hard, and push the primer button and the motor loads up.

To date, I've checked compression (120#, 130#, 125#), cleaned and adjusted carbs, replace fuel filter on the motor and on the water separator, and fuel lines (the inner liner had collapsed on some, restricting fuel flow), replaced regulator / rectifier, rebuilt the fuel pump, new plugs, tested plug wires (each had continuity) and tested the coils (all checked within spec).

When I pull the plugs, #1 looks "clean", while 2 and 3 have some normal carbon build up. I have confirmed that each carb is filling properly with fuel (50:1 mix). Using the timing light at idle, I have confirmed that each plug is receiving fire from the coils.

There's no excessive smoking (other than the usual Force amount)and no weird noises coming from the motor, other than the vibration and stuttering when accelerating.

So, I am at the point where I am out of ideas. Hopefully, someone on this forum will have a suggestion as to where to go from here, short of replacing the motor with a Yamaha.

Thanks in advance for your attention.

 

[Bannister 6905]

Also, I did confirm that the throttle control is fully opening the butterflies on the carbs and that they are fully closed at idle.

 

[Redbarron%%]

Get a clamp on ignition timing light and test it on all plug leads.
I had a similar problem and had a bad or intermittent trigger coil.
#1 may not be firing due to bad trigger coil, box , wire, plug, or ?
One way to check is to ground all of the spark plugs so that they generate current when they discharge and then check with the timing light for that discharge,
I had a similar problem made worse with water getting into #3.
The ignition problem (found after the water problem was fixed) was that bad trigger coil.
By the way I am not familiar with the outboard, but rather I have a Sport Jet,
With all of the troubleshooting and complexity of the old system I upgraded to the Mercury CDM coil/electronic packs and a harness from a three cylinder Mercury. You can do that it you have a red stator. The CMD s will work with the red stator and the earlier trigger coil and flywheel.

 

[Bannister 6905]

My 90 has the updated coil packs and i replaced the R/R, since it was clearly toasted. I've already confirmed the coils are firing the plugs by using my timing light. Thanks for your input.

 

[pnwboat]

If #1 plug is "clean" as compared to the others, there's a good chance that it is not firing.

Take a close look at the wires that come from the trigger assy. The trigger assy. moves as you advance the throttle forward to advance the timing. Sometimes the wires on the trigger assy. rub against the block and wears through the insulation exposing the bare wires and only shorts out when the throttle is in a certain position.

The other thing to check is a broken wire right at the strain relief where the wires come out of the trigger assy. itself.

You might be able to check for spark with a timing light with the throttle advanced in the Neutral fast idle position.

 

[Bannister 6905]

Excellent suggestion - will check this afternoon. Thanks a bunch!

 

[Bannister 6905]

OK, so I did as PNW suggested. I connected my timing light to each of the plug wires, started the boat, and watched for fire while I revved the motor (on the hose in my driveway). There were no indications at all of a misfire. The motor sounded strong and ran better than previously. I also checked the wires from the trigger and they were intact, with no sign of rubbing on the block, at least not through the insulation. I did "wiggle" the wires a bit during my inspection, so...?
No sign of air in the fuel line (clear amber) between the carbs and no leaking under the cowl.

The weather is turning again tomorrow, so no good chance to go to the lake until after Xmas...

A clarification question for PNW...just so I know I am looking at the right wires, these are the ones that come from the trigger and connect to the regulator / rectifier, correct? If so, these did not move when I advanced the throttle. The other 2 wire bundles, coming from the stator, I imagine, did move a lot, but I could not inspect them because I do not have a puller to remove the flywheel.

Again, thanks for all the help!

 

[Bannister 6905]

I tried to upload a video of the motor idling, but couldn't get the fine small enough (is 4mb max is 2mb). Very smooth.

 

[Bannister 6905]

"file"

 

[Redbarron%%]

If you needed to pull the flywheel you can "rent" one from most autoparts houses for $0.00, just a deposit.

 

[pnwboat]

The wires that go to the regulator/ rectifier are windings in the stator, not the trigger. The trigger wires go to each of the coils packs (if you have the CDM Ignition system).

 

[jerryjerry05]

The 95 came with Mercury ignition.
The connectors are known for going bad after some time.'
Unhook and clean the ends and reconnect with dielectric grease.
Also the prime/choke system can go bad(diaphragm) and feed excess fuel
to the carbs and cause the symptoms you describe?
The following is from outboardignition.com

If the cylinders are only acting up above an idle, connect an inductive Tachometer to all cylinders and try to isolate the problem cylinders. Check the trigger resistance and DVA output as given below:
	Wire	Read To	Resistance	DVA
	Brown wire (#1) White wire (#2) Purple wire (#3) Brown wire (#1) White wire (#2) Purple wire (#3)	White/Black White/Black White/Black Engine GND Engine GND Engine GND	800-1400 800-1400 800-1400 Open Open Open	4V or more 4V or more 4V or more 1V or more (a) 1V or more (a) 1V or more (a)
This reading can be used to determine if a pack has a problem in the triggering circuit. For instance, if you have no fire on one cylinder and the DVA trigger reading for that cyli?lder is low — disconnect the trigger wire and recheck the DVA output to ground from the trigger wire. If the reading stays low — the trigger is bad. Check the DVA output on the green wires from the switch box while connected to the ignition coils. Check the reading on the switch box terminal AND on the ignition coil terminal. You should have a reading of at least 150V or more at both places. If the reading is low on one cylinder, disconnect the green wire from the ignition coil for that cylinder and reconnect it to a load resistor. Retest. If the reading is now good, the ignition coil is likely bad. A continued low reading indicates a bad power pack.
Engine will not rev beyond 3000-4000 RPM: Connect an inductive Tachometer to all cylinders and try to isolate the problem. A single cylinder dropping fire will likely be the switch box or ignition coil. All cylinders acting up usually indicate a bad stator. Connect a DVA meter to the stator’s Blue wire and do a running test. The DVA voltage should jump up to well over 200V and stabilize. A drop in voltage right before the problem occurs indicates a bad stator. (Blue to Engine GND if the engine has a Red stator kit installed). Connect a DVA meter to the Red wire. The DVA voltage should show a smooth climb in voltage and remain high through the RPM range. A reading lower than what is on the Blue wire indicates a bad stator.
High Speed Miss: Connect an inductive Tachometer to all cylinders and try to isolate the problem. A high variance in RPM on one cylinder indicates a problem usually in the switch box or ignition coil. Occasionally a trigger will cause this same problem. Check the trigger as described above under “No fire or Intermittent on One or More Cylinders”. Perform a high-speed shutdown and read the spark plugs. Check for water. A crack in the block can cause a high speed miss when the water pressure gets high, but a normal shutdown will mask the problem. Remove the flywheel and check the triggering and charge coil flywheel magnets for cracks or broken magnets.

 

[Bannister 6905]

Issue resolved - switch box was going bad and finally failed. upgraded to the red stator, replaced the switch box and now it runs like a champ again. Thanks to all for your help!

 

[jerryjerry05]

Glad it's working!!

 

[72k5mike]

bannister, sorry to hijack your thread. I have a question about your boat as mine is exactly the same. What max rpm and max speed are you hitting? I just want to see if I’m in the ballpark with 29mph

 

[kbh121956]

To old of a thread. You would be better off to start a new one. The Mods will shut this one down.

 

[jerryjerry05]

90 hp. on a 17ft.
Should get 35 mph maybe more.
What rpm's are you getting?
What prop?
Your trim@tilt work?
How big a load ?

Bannister might not monitor this site as his boats fixed?