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1972 Johnson 100 MSD Ignition Conversion

T

THIRSTYLOTUS

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[FONT=&quot]Background: Last week I purchased a 1972 Crestliner with a Johnson 100ESL72R for $450. The engine had no spark which is why it was so cheap. I have gone through all of the steps to determine the issue and it is the power pack. A power pack is about $350 and breaks often. So I put an msd ignition box on it since they work better and are much cheaper.[/FONT]
[FONT=&quot]So I have hooked up everything together and the box doesn't fire with the stock crank trigger sensor. This perplexes me since this should be a magnetic pickup, as it has 2 wires and a ferrous wheel with lobes corresponding to the timing. I check the sensors resistance the other day and it was within spec so i dont believe it to be broken. Does the sensor output a lower voltage then the msd box wants to see? Or is there something else making the sensor and the box not work together? Any help would be great.[/FONT]
 
My computer is busted, so I don't have all my info on hand. But from memory, I think that '72 has a Hall effect sensor and does not generate a voltage. If I am wrong, beat me and ignore this.
 
fdrgator said:
My computer is busted, so I don't have all my info on hand. But from memory, I think that '72 has a Hall effect sensor and does not generate a voltage. If I am wrong, beat me and ignore this.
Click to expand...

I do believe it's a magnetic sensor not a Hall effect. Since it has 2 wires (Hall effect generally have 3) and a ferrous metal reluctor wheel in front of it. A magnetic sensor senses the change magnetic flux, which a reluctor induces. A Hall effect sensor measures the strength of the magnetic field it is in. So they generally have a magnet placed behind a wall that rotates with the crank, the wall has cut outs in it to allow the sensor so get a square wave inorder to fire the cylinder. So unless they did something odd, which is entirely possible, I would say it's a magnetic pickup.
 
Excellent explanation, Lotus. Do you have a DVA? I have a 10 year old analog type, (entire meter), only 100 bucks. Use it constantly. For those following along that may not know what we are talking about, this type of a meter or adapter will measure the crest or peak of the voltage instantaneously. This device is primarily used in the Marine industry and for measuring and diagnosing capacitive discharge ignition systems (for lack of a more specific definition).
 
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Before I take the beating, I admit you might know more about hall effect than I do. I'm not sure that is even the correct terminology here. BUT according to my understanding (??) the pulse pack sends a voltage to the non-magnetic sensor, which magnetizes it. The the notched rotor interrupts the magnetic field as it passes, changing the resistance, which is detected by the pulse pack. No, I don't think it generates a voltage. Let the beating begin now.
 
Thank you, my 4 years of studying physics is finally paying off lol. I have one of the adapter DVA units for DMM but it wasn't giving me a reading. I do have an oscilloscope but it doesn't work all that well, so I'll try to rig it up so I know it will give me a reading (if there is any) but if I can't I could probably borrow one from the college I work at.
 
No beating, Gator......you probably know more about this than you lead on. Just going on memory, however, it's hard to accurately navigate sometime. Just think how many boaters out there are helped by your knowledge.
 
Well I dont think this sensor will ever play nice with my msd box. But I know the points engines do work. So what components would i need in order to convert the engine to points?
 
Take a good look at the crankshaft.-----Some had the cam for points ground on them.----Then you have to find the timer base and points from a 69 / 70 V-4 85 or 100 HP.-----Easy to find those items in some areas.
 
Try Tim's Outboard Hackensack MN 218 682 2331. I have been hunting and fishing in remote areas since a child, and honestly I say to you, have never been stranded by an analog/mag/points ignition system. Electronics and CDI's..........have made me troubles with NO WARNING!
 
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Alright so I completed the instillation of an MSD ignition box. I converted it to points and everything was great. The spark was nice and bright! I used 1 high vibration coil, that has a .8 ohm resistor in series with it (The resistor lowers the input voltage to the coil from 450V to about 310V). The engine started up really nicely and fast, and had a nice idle. Every thing was looking good so I took it on the water.

This were where I had some issues. first off the throttle cable was suck so I could not go past idle. This was actually a good thing since after about 10m the engine shut off and would not start back up. It seems as if the engine is not firing on the right cylinder from time to time making it not start and work against its self. We didn't have to row far since we were only going like 4mph.

I removed the stater to take a look at it and it has cracks between each contact point in the distributor portion of it which is what I believe is giving me the problem. The rotor looks good, no signs of melting or anything.
 
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