1971 80hp Merc suddenly stops under full power

[wemertz]

I had my boat out yesterday, and under full power, the engine just shut down.
Fortunately, no one was hurt!
The engine restarted OK.
I was wondering what might have caused this.
I have disconnected the Mercury switch.
The internal wires are in poor shape, so I've just ordered a new internal wiring harness.
It still seems something else might be at fault, like a grounded kill switch or something.

Any help would be greatly appreciated.

Wayne

 

[Chris1956]

Re: 1971 80hp Merc suddenly stops under full power

Wayne, If that motor has distributor ignition, it must have battery voltage on two wire on the switchbox, in order to have spark. Since you know the engine wiring harness is bad, it is not much of a leak of faith to say that the power to the switchbox may have been interrupted.

 

[86RajunCajun]

Re: 1971 80hp Merc suddenly stops under full power

I had my boat out yesterday, and under full power, the engine just shut down.
Fortunately, no one was hurt!
The engine restarted OK.
I was wondering what might have caused this.
I have disconnected the Mercury switch.
The internal wires are in poor shape, so I've just ordered a new internal wiring harness.
It still seems something else might be at fault, like a grounded kill switch or something.

Any help would be greatly appreciated.

Wayne

IF you already know the internal wiring is in rough shape, i would check under the flywheel also, the wire coming out from under it, that is that stator and it acts pretty much like the alternator/generator for you igntion. they also generate the power that fires your coils. IMO, i would go through every single wire on the side of the engine one by one and replace any parts that are unserviceable due to wire breakage. This will likely be the only way you will have reliability in the future anyway. I had to do this on my 1986 mariner v6 150, and when i did, it ran like a beast till i sold it 2 years later.

Good luck sir.
RC

 

[Chris1956]

Re: 1971 80hp Merc suddenly stops under full power

RC, His motor should have a battery powered CDI ignition. The stator is a simple coil of wire which just charges the battery, via a rectifier. The ADI ign system you have on your motor was not used on the inline 4 Mercs until about 1975 0r 1976.

 

[wemertz]

Re: 1971 80hp Merc suddenly stops under full power

RC, His motor should have a battery powered CDI ignition. The stator is a simple coil of wire which just charges the battery, via a rectifier. The ADI ign system you have on your motor was not used on the inline 4 Mercs until about 1975 0r 1976.

Absolutely correct!, Found the stator wire worn through and was not working.
However, if Chris hadn't made his comment, I wouldn't have went to all the work of checking. Thanks very much to you all. Wayne

 

[1960 Starflite]

Re: 1971 80hp Merc suddenly stops under full power

RC, His motor should have a battery powered CDI ignition. The stator is a simple coil of wire which just charges the battery, via a rectifier. The ADI ign system you have on your motor was not used on the inline 4 Mercs until about 1975 0r 1976.

I have a 1975 85hp with the same CDI setup, battery driven ignition with distributor. It is on pontoon boat I rode on and bought. I pulled the engine and put on my stand since the wiring is toast!!!! I really don't know how it ran, all the insulation on the wiring is gone, yea, gone, bare wires everywhere.

Can someone tell me what the ohm reading should be across the two yellow wires coming out of the stator? Also, how I should check the rectifier? Previous owner said he had to charge the battery with charger. My Clymer manual doesn't call out this model.

BTW, Mercury went to the flywheel trigger in 1976.

 

[Chris1956]

Re: 1971 80hp Merc suddenly stops under full power

The Stator charging coil should be .3 Ohms. The rectifier is a bridge of 4 diodes. They will pass voltage in only one direction if they are good. So set the meter to ohm and test each adjacent set of contacts. Note the reading (o ohms or infinite ohms) and reverse the leads. The reading should switch as well.