72 Mercury 800 80hp 4cyl Ignition Issues

[Super Dragpack]

Hi all,

I have just purchased a circa '72 Mercury 800 80hp 4 Cyl outboard. I have a few questions but the first if the ignition system.

It has a basic system with a distibutor and coil etc and I have no spark.

The wiring is very poor so I am sorting the old wiring (got a wiring diagram from online) but its seems that the wires to the switch box are different than in the diagram. There are only 4 terminals on the switchbox but I can't work out what the box actually does on this motor.

The stator/altenator and rectifer are very seperate and not connected to the ignition system at all. The distributor has no points (electric HEI I assume) and only three wires coming from it.

So I have three wires coming from the dizzy (plus earth), 4 terminals on the switchbox, a coil (2 terminals) and a condensor (1 wire and earth). So in this type of very basic system, what does the switch box do?

How can I test the switch box?

How can I test the distributor ignition system (HEI)?

Thanks in advance.

Mick

 

[Moody Blue]

Re: 72 Mercury 800 80hp 4cyl Ignition Issues

Hi all,

I have just purchased a circa '72 Mercury 800 80hp 4 Cyl outboard. I have a few questions but the first if the ignition system.

It has a basic system with a distibutor and coil etc and I have no spark.

The wiring is very poor so I am sorting the old wiring (got a wiring diagram from online) but its seems that the wires to the switch box are different than in the diagram. There are only 4 terminals on the switchbox but I can't work out what the box actually does on this motor.

Your ignition requires two things to be able generate spark.

On the PORT side of the switchbox there should be constant +12 on the RED terminal AND +12V on the WHITE terminal with the key on.

The GREEN wire from the coil connects to the GREEN terminal.

The BROWN wire if there is one, is not required and can be disconnected or left connected.



The stator/altenator and rectifer are very seperate and not connected to the ignition system at all. The distributor has no points (electric HEI I assume) and only three wires coming from it.

That is correct. Only function of the stator is to keep the battery charged so that the ignition system will function. It is called a battery CDI (capacitive discharge ignition). Those three wires are the trigger wires. The trigger circuit in the dist housing sends the signal to the switchbox WHEN to fire. The

So I have three wires coming from the dizzy (plus earth), 4 terminals on the switchbox, a coil (2 terminals) and a condensor (1 wire and earth). So in this type of very basic system, what does the switch box do?

That condensor is actually a mercury switch. If you tilt the engine too high it kills the ignition. A safety feature to save the engine from over-revving if the prop comes out of the water.

The switchbox sends a voltage pulse to the coil at the appropriate time. The coil then generates the high voltage that is send to the plugs via the distributor

How can I test the switch box?

There is a good write up on this forum. Search for CDI test, or switchbox test. There are a few places listed below that have good instructions.

http://outboardparts.com/mercury/troubleshooting/troubleshooting8.htm

http://www.boatpartstore.com/page18.asp

http://www.maxrules.com/cdi/TroubleshootingGuide.pdf


How can I test the distributor ignition system (HEI)?

See above.


Thanks in advance.

Mick

Good luck.