1972 50hp Johnson Ignition Problems

[Big Bird]

I am trying to revive an older motor and can not get a spark on either of the two cylinders, even with the kill wire disconnected. The Stator resistance (wire connected to power pack) is good (reads 480 ohm, book calls for 500 ohm) but the output voltage is low (reads 46V, book calls for 150V min). The Timer Base resistance reads open (wires disconnected from the powerpack)when it should be 10-20 ohms, and the output voltage is a little low (reads 0.4V, book calls for 0.5V min). The trigger wires read 300V, the book calls for 150 min. I have not checked the Power Pack or Ignition Coils as I do not have the needle point spark checker or a S-80 or M80 neon test light that the service manual calls for. Since I have obvious problems upstream I plan on waiting to check out the Power Pack and Ignition Coils. I do not want to throw away cash on special tools like wheel pullers and expensive parts unless I know that it will fix my problem. What would be the logical next step in diagnosing this problem?

 

[Big Bird]

Re: 1972 50hp Johnson Ignition Problems

I forgot to mention that the battery is new and fully charged, my problem is not starter RPM.

 

[tashasdaddy]

Re: 1972 50hp Johnson Ignition Problems

test. http://www.boatpartstore.com/page29.asp

Hydro Electric Shift)
(J. Reeves)

The shifting setup of the lower unit is what's called a "Hydro Electric Shift", which is quite complex consisting of voltage being applied to solenoids in the lower unit which in turn change oil passages via a oil pump that supplies various pressure on a spring loaded shifter dog. The wires leading to the lower unit (at the powerhead) are "Green" and "Blue". The engine must be running or cranking over in order to shift out of forward gear.

You CAN NOT use HI VIS lube in that lower unit. You MUST USE what OMC calls "Premium Blend" lube, commonly called "Type C". (A thinner lube)

In neutral, you need 12v to the "Green" wire.
In reverse, you need 12v to both wires, the "Green" one and the "Blue" one.
In forward, there should be no voltage to either wire. (The spring loaded shifter dog forces the unit into forward gear)

To check the lower unit for proper shifting to make sure you have no trouble there, remove the spark plugs to avoid problems and to allow a higher cranking speed.

This next step eliminates the actual shift switch in case problems may exist there.... Disconnect the blue & green wires at the knife connectors (the rubber insulated boots) leading to the lower unit at the powerhead, then using jumpers, take voltage direct from the starter solenoid to apply voltage to the "Green" wire for neutral, then both wires 'Green" & "Blue" for reverse (Remember the engine must be cranking over in order to shift).
With no voltage applied, the unit should be in forward. No need for a ground jumper... the lower unit's already grounded. You may crank the engine with the key switch or by energizing the starter solenoid with a jumper wire.