boat wont start in water but starts in driveway everytime

Help,
1972 50 hp Johnson with hydro electric shift 50272C Outboard Motor will start every time in the driveway, but just won’t start in the water.
Compression is good, 155 top cylinder, 150 bottom cylinder. Plenty of bright blue spark.
Carburetors overhauled. Pumps great water.
Changes gear in both directions in the bin of water.
Outboard is clamped to the tinnie hull, so I would assume its grounded ok?
The only thing I do know, is that if I run the boat in the driveway with muffs on, and also immersed in a large bin to keep noise down for neighbours, I got a spare length of wire, and touched it from the De Havilland aluminium hull and placed the other end on the leg of the outboard. There is a spark there, and if I hold the 2 ends in place it acts like a kill switch and stops the motor.

Does anyone have any idea maybe what is going on please?

Pretty sure that I answered this in another sites forum, however.................

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(Engine Won't Start or Hard Starting In Water)
(Joe Reeves)

The Evinrude and Johnson engines, starting in 1973, have what is called Magneto Capacitance Discharge ignition, self contained, not dependent on battery voltage. The engine must turn over at least 300 rpms in order for the flywheel magnets rotating past the stator ignition generating coils to supply approximately 300v AC to the powerpack(s), which in turn is needed to supply power to the coils etc etc (spark).


In the water, exhaust back pressure is encountered due to the fact that the exhaust housing (housing between the powerhead and the lower unit) is filled with water. This would drag down the needed rpms, affecting ignition.

Normally the clue to this type problem is that the engine starts fine on a flushette (hose), but is very difficult to start when in the water.


Should this be the case, check the battery, clean and tighten all conections (use a wrench or pliers, not your fingers). Any cable that gets overly warm or hot indicates either a loose, or tight but dirty, or internally corroded cable. And of course check the starter itself.

Hi Joe,

I have read this in your other post, which is why I had the outboard also in a large bin water, to mimic sea conditions.
But it's the electrical problem thats stopping spark. Not the fact it turns slower, which it really doesn't for this old girl.
I have just had the motor in the bin of water also, without muffs! I also tried the water deeper than it would be at sea to try to make more pressure.
but in the sea, if I pull out the spark plugs while still floating, there is no spark at all!
I got a spare length of wire, and touched it from the De Havilland aluminium boat hull and placed the other end on the leg of the outboard. There is a spark there, and if I hold the 2 ends in place it acts like a kill switch and stops the motor.
The motor is clamped directly to the boat, so should be plenty of earth!

Disconnect the black/yellow stripe wire from the powerpack and see if you still have the issue. If you need to kill the engine just short the black/yellow wire on the pack to engine ground

The solution is simple, move to Ontario and fish Oligotropic lakes only. You might try some early stage mesotropics too. Just keep a set of oars with you.

Fresh pristine water does not conduct electricity. Guess that's why I've never seen this problem here in northern MN.

Paul... In post 1, you state "Plenty of bright blue spark".

In Post #3, you add "but in the sea, if I pull out the spark plugs while still floating, there is no spark at all!"

That rig would go well with the Poltergeist movies.

Paul, you have a problem outside my capacity, Mr. Reeves can help you. My customer just called, I gotta get to work, burning my bills in the stove doesn't work anymore. Why is this guy coming every month in a little blue car to take a picture of our house?

Hi Joe

Yes, you may be well right, the motor is possessed however I am sure this demon motor will eventually start in the salt sea! lol

I will hopefully try what Kimcrwbr1 mentioned Disconnect the black/yellow stripe wire from the powerpack and see if you still have the issue.

Hopefully the demon motor does not ignition pack me with a hi voltage shock!

Seriously now what has happened is that the kill wire is shorted somewhere beyond the engine itself giving it continuity to the body of the boat. and the motor body itself is not completely grounded to the boat hull. The problem is likely in the ign switch or control itself. The small ground wire in the rear port side of the Powerhead, ( I think that's where it is on this motor), is likely not connected between the Powerhead and the outer cowling base. If it was you would have no spark because everything would be grounded by the shorted kill switch.
It was fun helping you, what do you think of these techs here?

Thank you all, Kymcrwbr1, Timguy and Joereeves, spot on with issues why this demon motor wouldn't start in the sea water, disconnected the yellow and black wire, and BOOM motor would not stop by running a wire between tinne and outboard! Tried again with yellow/black wire on, and it stopped. So left the yellow/black wire off, down to the boat ramp, outboard started 2 pop. took it for a blast down the river! perfect! So a huge huge thank you for all your help!

Paul... Normally, disconnecting the black/yellow wire (kill circuit) from the power-pack to have ignition (spark) return to the engine indicates either a internal short within the ignition switch OR a short at some point with that black/yellow wire... BUT... that shouldn't matter whether the boat is in the water or a trailer, and in this case, it obviously does.

Apparently the problem is due to the boat being aluminum instead of wood or fiberglass... BUT... there are many aluminum boats out there whereas this problem does not exist.

Wondering...... The raised "M" terminal of the ignition switch should have just this one lonely black/yellow wire attached and no other.... with the other "M" terminal having just the one black wire leading to ground. Any other wires attached creates weird happenings... perhaps this one?

To lose ignition/spark in the manner explained here... only when the aluminum boat is in the water... that black/yellow wire's conductivity would need to be somehow grounded to the aluminum boat with the conductance traveling through the water to the engine's lower unit which would effectively ground (short out) the power-pack kill circuit.

Since this does not take place with the rig on a trailer, a regular ohm meter connected between the disconnected black/yellow wire at the power-pack (the wiring harness side) and the aluminum boat should show up the short (key in ON position, engine NOT running)...

Finding the exact location of that short is another matter. If you find it, let us know.