1987 Mercury Outboard, shuts down after going wide open - see video

[puckoach]

I have a 1987 70hp Mercury on my Mariner recently if I go wide open it will cut out and stall after a few hundred feet, I thought it was a fuel issue so I put all brand new fuel lines on, about 30 bucks worth, I also installed new spark plugs, I even went as far as getting a compression tester, I got 90 lbs in each cylinder

I have a fuel selector switch which controls 2, 5 gallon tanks under the seat, today when it kept shutting down I tried selecting the other tank and it did the same thing

and after it shuts down its hard to start I have to give it like full throttle in neutral for it to start

the vents are wide open on the fuel caps also

I made this video today so you can see what I'm talking about, I didn't touch the throttle at all when it was shutting down

Mercury outboard shutdown - YouTube

I guess the next thing I'll try is to run a gas line from the tank to the motor, without the selector

 

[64osby]

Re: 1987 Mercury Outboard, shuts down after going wide open - see video

Might be better to post in the Merc forum. Lots of knowledge over there.

Try running on different tank, check the fuel pump (might be getting weak)

 

[puckoach]

Re: 1987 Mercury Outboard, shuts down after going wide open - see video

ok thanks, didn't know there was a mercury section

 

[puckoach]

Re: 1987 Mercury Outboard, shuts down after going wide open - see video

anyone have a pic diagram of where the fuel pump would be, Id like to check it out, have no idea where it is

 

[Gibbles]

Re: 1987 Mercury Outboard, shuts down after going wide open - see video

best bet is the merc forum, but I have a few old mercs...

First question I would like to know... what does the engine do when it "shuts down"?

like does it just straight shut down, or does it sputter, loose power, and then shut down?

Sputter's and shuts down, could be fuel pump (can't miss the hoses that go into the side of the engine, back out, and into the carbs).
Also could be a plugged fuel filter or screens.

I had some rust hit my pre filters (I installed them), under full it would force it up and plug the filter, engine would loose power, I would stop, and it would try to keep running... then die.

Another common issue with those old mercs, the plug that goes to the ign s witch on the side of the engine.
Very common for those plugs to get all corroded.. volt meter set to check ohms from the ign switch wires, to the wires on the switch box.


edit: just watched the video, strange... can you start it right up after it shuts down?
touch the top of the engine (above sparkplugs), is it really hot or just warm?

Check the wire plug, ensure fuel system is clean, bypass the selector switch, you should have a factory filter under the cowel, check it.

 

[shipoffools]

Re: 1987 Mercury Outboard, shuts down after going wide open - see video

Ok here a possibility from my long list of weird things that have happened to my 88 Mercury 70. There are plastic retainer pins that hold the one way valves in place inside the fuel pump. one of them broke off and found its way into the fuel inlet on the top carb. If i shut it down and messed with it it would start up and run again until I opened it up to full throttle then the piece would jam back into the inlet. At the time there was no filter between the fuel pump and carbs. after a miserable afternoon trying to fish the piece out of the carb I rebuilt the fuel pump and added a small filter between the pump and carbs.

 

[puckoach]

Re: 1987 Mercury Outboard, shuts down after going wide open - see video

holy crap I think I found out my issue, and I have no idea how my motor is still running

took the covers off to check on the fuel pump and found this broken hose line that goes to it

I was looking everywhere for the broken hose and finally found where it was coming from, the other end is right where the oil injection hose hooks to, you can see the other nipple below it, somehow both ends broke off and there's no hose

 

[puckoach]

Re: 1987 Mercury Outboard, shuts down after going wide open - see video

http://oi41.tinypic.com/357jcdh.jpg