1995 90 HP Mercury Outboard - runs for a while then shuts down

JamieClay

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I posted earlier about this motor starting up running briefly then shutting down and that was solved with a fuel feed pipe repair.

However a new problem (seemingly) occurs. Poor idle, runs under load for a while then dies out.

I've replaced the fuel filter, checked all hoses and everything looks in order.

When it dies out, if I manually squeeze the primer bulb it will often fire back up. Maybe the fuel pump is failing or there is restricted flow leading to it.

It'll run for 15 or more minutes at slow speed before stalling out.

Any tips as to what to look for are appreciated! Thanks.

Jamie
 

ondarvr

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Re: 1995 90 HP Mercury Outboard - runs for a while then shuts down

Possible fuel pump issue, but check for air leaks in the fuel line first, the "O" rings in the connections are a normal failure point.
 

JamieClay

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Re: 1995 90 HP Mercury Outboard - runs for a while then shuts down

Possible fuel pump issue, but check for air leaks in the fuel line first, the "O" rings in the connections are a normal failure point.

Thanks - wouldn't air leaks also behave as fuel leaks when I pressurize the system via the primer bulb? I'm pulling it out of the water this morning and going to go over all the fuel leads on shore.
 

ondarvr

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Re: 1995 90 HP Mercury Outboard - runs for a while then shuts down

Possibly, but if they are before the primer bulb they wouldn't be under pressure. Also some of the leaks stop when under pressure, especially when it comes to O-rings
 

philipjames5k5

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Re: 1995 90 HP Mercury Outboard - runs for a while then shuts down

I had a bad primer ball, It would get hard and lose its prime after started which made the engine cut off. It seemed to be a good primer ball but I switched it and it worked fine. Just something cheap you may want to try if you have not already.
 

JamieClay

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Re: 1995 90 HP Mercury Outboard - runs for a while then shuts down

I had a bad primer ball, It would get hard and lose its prime after started which made the engine cut off. It seemed to be a good primer ball but I switched it and it worked fine. Just something cheap you may want to try if you have not already.

I think replacing the primer ball isn't a bad thing to try. If it is restricted then that would make some sense to how this is behaving. It might even be a restriction that fluctuates.

One interesting note, when we first launched the boat, we managed to flood the engine via over priming. I can't seem to do that now. I'm not sure if there is a direct correlation but that's one thing I can't seem to duplicate.

I like this theory because right now it makes the most sense. If there was an air leak after the primer then I would expect fuel to leak when the system is pressurized. But a restriction in the primer itself would play well into the load failure.

I'll let you know, thanks!!
 

JamieClay

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Re: 1995 90 HP Mercury Outboard - runs for a while then shuts down

So the Moeller primer bulb looks very new as well as the hoses attached to it and to the tank.

I removed the line at the NPT connector and the fuel flowed nicely. Mind you it it may develop a restriction when under heavier demand and replacing it would be cheap (I just couldn't find one today)

I'm also suspicious of the NPT connector as I can see the potential for that causing a flow restriction.

I'll post more as the plot twists.

Thanks again!
 

philipjames5k5

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Re: 1995 90 HP Mercury Outboard - runs for a while then shuts down

My bulb seemed fine and all the lines and connectors seemed fine as well. The bulb primed and got hard before turning the motor over, but once the motor was started the bulb would lose prime causing the motor to hiccup and finally die. This may not be your problem, but it fixed my issue. It seems its either not getting the fuel or it is getting air into the lines. I would replace all fuel hoses, clamps, bulb, and connectors. I change these every winter just to keep them fresh, and new.
 

CharlieB

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Re: 1995 90 HP Mercury Outboard - runs for a while then shuts down

The other poster was trying to explain that the O-ring in the fuel fitting to the motor can seal perfectly when pressurized by the primer bulb but once running the fuel pump SUCKS on that O-ring, and can suck in air. Thus the motor simply runs out of fuel at low speed. Running faster the pump still manages to pump enough fuel to stay running.

The dangerous part of this is running at WOT, the upper carb may not be kept full and that cyl can go lean, melting a piston.

A quick test, replace the fuel hose from the fuel pump to the carb with a clear hose. Run the motor and watch for a regular stream of air bubbles, proving air sucking in.

REMEMBER, remove the clear hose once finished with repairs, it is ONLY a temporary testing tool. Clear hose is NOT rated and is NOT recommended for fuel use. Only a very short term testing tool.
 

JamieClay

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Re: 1995 90 HP Mercury Outboard - runs for a while then shuts down

A quick test, replace the fuel hose from the fuel pump to the carb with a clear hose. Run the motor and watch for a regular stream of air bubbles, proving air sucking in.

REMEMBER, remove the clear hose once finished with repairs, it is ONLY a temporary testing tool. Clear hose is NOT rated and is NOT recommended for fuel use. Only a very short term testing tool.

Gotcha - I'll try that (need to get some clear line).

I'm also going to change the primer bulb anyway - just couldn't find a marina with one today. (Marin County, Ca has so few good ones)
 

JamieClay

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Re: 1995 90 HP Mercury Outboard - runs for a while then shuts down

I've a question about the Oil reservoir for this motor, is it pressurized? (still hunting down the manual) and if so would the loss of pressure result in the motor shutting down? Does the level of the 2 stroke oil affect the operation, in example I know the generator on my motor home will shut down when the oil is too low.

I found the fill plate on this motor to be leaking when the motor was fully tilted back, the latch wasn't securing properly, the reservoir was half full.

Also, how likely is it that the fuel pump is sporadically failing?

The fuel system seems solid up to the pump, I've still not had a chance to try the clear fuel hose test (CharlieB) but plan to soon (waiting on the hose).

I doubt this picture would help any, but here is the side of the motor where all the fuel routing is.
Merc90Fuel.jpg

Oh and is there a chance the Enricher Valve could be causing this behavior? From the name, it sounds like something that influences the fuel flow.
 
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Toddboat

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Re: 1995 90 HP Mercury Outboard - runs for a while then shuts down

Fuel enrichment system is only there to help start the motor when cold. It should have no effect once the motor is warmed up. It is a needle valve. I suppose if it is stuck open, it could flood the motor. You could rule it out by disconnecting it and seeing if you still have the same symptoms. Change the membrane in the fuel pump. Make sure your tank is vented.
 

JamieClay

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Re: 1995 90 HP Mercury Outboard - runs for a while then shuts down

Fuel enrichment system is only there to help start the motor when cold. It should have no effect once the motor is warmed up. It is a needle valve. I suppose if it is stuck open, it could flood the motor. You could rule it out by disconnecting it and seeing if you still have the same symptoms. Change the membrane in the fuel pump. Make sure your tank is vented.

Well it does idle poorly - however that isn't the primary problem. It looks like replacing the membrane on the pump would be inexpensive and straight forward.

Thanks.
 

Boanyard

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Re: 1995 90 HP Mercury Outboard - runs for a while then shuts down

FYI...there is clear fuel line. new ethanol resistant line comes in various colors. i have blue, yellow and clear in the shop now. I will find out where we got it and who makes it and let you know.
 

JamieClay

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Re: 1995 90 HP Mercury Outboard - runs for a while then shuts down

FYI...there is clear fuel line. new ethanol resistant line comes in various colors. i have blue, yellow and clear in the shop now. I will find out where we got it and who makes it and let you know.

Thanks - that could be helpful - it's still that last thing I've yet to try. As of this last test I replaced the primer bulb and rebuilt the fuel pump. The pump showed the most promise. (see the included picture)

After these changes, it the problem still seems to be occurring, mind you I'm testing it out of the water so maybe it's just not fully warmed up. I'm unsure. Maybe I have two problems - one where I can't get it to idle and the other high volume fuel draw. One thing for sure, the pump diaphragms and gaskets looked like crap. IMG_0164[1].jpg

I should mention the pump rebuild kit came with thin plastic valves instead of the rubber ones that were installed. I'm not a fan, they just don't look like they would seal as well.
 
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JamieClay

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Re: 1995 90 HP Mercury Outboard - runs for a while then shuts down

Another question - is this pump vacuum driven? I don't see any mechanical actuator when I take it apart. Also note the online parts catalog shows two parts to the check valves where the replacement kit only shows the one.

It seems likely the online catalog is showing optional parts but in this case it actually doesn't list the names for the check valves (no doubt because they are included in the gasket set)

fuelpump.jpg
Catalog listing
 
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CharlieB

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Re: 1995 90 HP Mercury Outboard - runs for a while then shuts down

FYI...there is clear fuel line. new ethanol resistant line comes in various colors. i have blue, yellow and clear in the shop now. I will find out where we got it and who makes it and let you know.

NONE of the vynal(spelling?) 'clear' fuel hoses, whatever tint, none are CG approved fuel hose, NONE will pass the 'burn thru' time test and all are considered UNSAFE for marine applications.

They are great for weed wackers or any other motor used on land as you can simply walk away when/if they fail.
 

JamieClay

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Re: 1995 90 HP Mercury Outboard - runs for a while then shuts down

NONE of the vynal(spelling?) 'clear' fuel hoses, whatever tint, none are CG approved fuel hose, NONE will pass the 'burn thru' time test and all are considered UNSAFE for marine applications.

My only intention is to use it to diagnose the problem, I don't plan to use it permanently. I also picked up a clear glass fuel filter so I can observe the flow - again only to be used for diagnosis.

One thing I didn't do when I replaced all the pump diaphragms was to replace the base gasket to the pump. Realizing now the pump must be activated by some sort of vacuum or air pressure (not sure which) I can see where it might fail to deliver if that gasket was leaking. So I have that to try as well.
 

JamieClay

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Re: 1995 90 HP Mercury Outboard - runs for a while then shuts down

New developments in regard to this. After a discussion with a local Mercury Outboard mechanic, he confirmed the fuel pump operates on crankcase pressure and that pressure can be lost if the oil reservoir top isn't secure. One problem this motor has IS the oil reservoir filler hatch doesn't seal (if I tilt the motor back it leaks).

So I've got a new gasket on order. I think I'm getting closer to solving this.

Oil Fill.jpg
 
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