My 1992 Mariner 90elpto is sick...puzzled

[Bannister 6905]

Motor - 1992 Mariner 90ELPTO S/N OD130152

Up until a recent trip to MN, the boat has run well, with no issues. During the trip, I drove through a deluge and apparently water got into the fuel, which caused the motor to run poorly. I eventually drained the tank and refilled with known good gas, but the running issues continued. The symptom was stalling after being underway for a short time. Afterwards, the motor would start up, but was difficult to keep running

Symptoms - hard to start, as if the motor is starving for fuel. Once running (rough), it gradually slows to running on one cylinder and then stops. It will not accelerate while in the water above a fast idle, and eventually dies again.

The strange thing is that it runs pretty well (although a bit rough) on the hose in the driveway, never stalls and seems to accelerate up to 2000rpm with no problem. On those occasions when the motor starts to slow down when on the hose, I spray carb cleaner into #2 or #3 carb intake and the motor picks right back up - it often just keeps on running well after that.

Aside from replacing the fuel, I have done these things:

new fuel lines
rebuilt fuel pump
new plugs
new filter
removed and cleaned carbs twice - they are clean
replaced intake carb gaskets
checked for leaks around carb shafts, hoses, fittings - sprayed with carb cleaner with no effect.
new 16A stator (old one was failing tests)
confirmed all 3 cylinders are firing when motor dies (by timing light)
checked for "spitting" from carb intakes - nothing (reeds)
compression reads 120 / 120 /115 - motor warm, throttle wide open
trigger tests OK
rebuilt water pump - strong stream and motor runs at normal temp when on the hose. Strong stream when in the lake, as well.

On both occasions when I removed the carbs for cleaning, all 3 had fuel in the float bowls and the floats did not appear to be sticking and there were no restrictions in the lines or elbows feeding the carbs from the fuel pump and between the carbs.


When on the water, the only way to get the motor to even go a bit is to depress the primer on the key switch, which allows the motor to speed up a bit, but it will not plane the boat (17' Fisher aluminum) and quickly dies. During this time, the primer bulb remains hard. Pumping the bulb has no effect on the motor stalling.

I've know of reached a stalemate with the motor and am out of ideas as to what the cause might be. Any suggestions would be appreciated.
Thanks.
Bannister

 

[Bannister 6905]

While in MN, I also ran the motor off an external tank to see if that would help - no difference or improvement.

 

[Texasmark]

Sounds like you did your homework. The test tank of fuel pretty much completed the process.....thinking while typing here......You mentioned things that you did that obviously weren't associated with running through a deluge...assume you mean it was raining hard, not that the rig was under water type thing.

On the 90 the linkage setup is a bit different and consulting a manual would help as would checking timing as detailed in the manual and idle is set by changing the timing with the knurled screw on the timing arm.....675 +/- 50 in the water in F gear, remote throttle at idle. Other thing is, by chance, check the little black plastic gadgets on the carb linkage to ensure that they are intact and don't move (slop due to wear or being broken) when the linkage is moved. Check the butterflies to ensure that they all move in unison as the throttle position is changed.

You are telling us that you are fuel starved with your other comments. When you did the carbs did you disassemble them completely? Did you blow out all the passages with compressed air? Did you find any little black specks in any of the carbs....signs of fuel line degradation? Do you have any signs of leaking fuel around any of the engine fuel lines, especially when squeezing the bulb....and it being hard....(saw that you mentioned that but look again)? Got the float level set correctly?

Could be a reed valve, but never heard of the flower reeds used in those engines (I had a 2002) failing. Gotta remember that 2 strokers need oil in the fuel and carb cleaners don't have that.....Sea Foam Aerosol does. Still thinking........

 

[Bannister 6905]

Thanks for the reply -

Yes, I drove through a super-heavy thunderstorm on the way north...i verified the fuel was wet by letting the boat sit overnight and then pumping fuel into a clear container and watching the water separate from the gas. The boat was not submerged.

When i cleaned the carbs, I went through them carefully and used compressed air to make sure all the tiny orifices were clean. The first time I went through them, they had a bit of debris in them, including what looked like black / brown sand built up in the elbow that feeds the lower carbs. I've seen that before on other 3-cyl mercs. Since each carb was full of gas when I disassembled them, I did not check the float heights.
Anyway, the second time through, just to make sure I had not missed anything, I repeated the process, including checking each and every hose and elbow to make sure they were clean, and they were. There are NO leaks anywhere and no sheen on the water if the boat is sitting and idling for a period of time. I also checked the discharge water from the telltale for oil/fuel and found nothing.
Yes, the bulb pumps up quickly and stays hard, even if the boat sits overnight. I've confirmed the anti-siphon valve in the tank is working properly, and I've even tried running the boat with the fuel cap off...no difference.

The linkages are all working properly and the synch is good, as well. There are no mechanical issues I can see. I've not checked the timing...as I said, before the rain storm, the motor always ran very well, with no issues.

The next thing i am trying is a new switch box. I'll update after a lake test tomorrow.

Again, thanks for your input.

 

[QBhoy]

Could you have run lean ? Is the oil mixed with fuel on your engine or still injection

 

[Bannister 6905]

Oil injection.

 

[Bannister 6905]

After today's trip to the lake (motor started ok, ran at speed for about 20 seconds and then died), I removed the carbs and found milky fluid in the intake (see pic) and water droplets inside the carbs and on the spark plug electrodes. I pulled the head cover off and found that the gasket had one large tear in it (see pic ) near the top cylinder, as well as several smaller cracks lower near the bottom cylinder...

I've ordered a new gasket, as well as a new thermostat kit and will try that. Any other ideas?

By the way, I did check the float levels and all 3 were at 7/16", at spec.

Thanks.

Bannister

 

[Bannister 6905]

Update: 15 Sep

Replaced the head cover gasket, serviced the poppet valve and replaced the thermostat (stuck closed), seal and housing gasket. Readjusted the low-speed setting on the carbs (to 1 3/4 turns open), set initial timing and the motor now runs like a champ.