Troubleshooting a 1972 Johnson 100hp

[pitprice]

I have recently purchased a cheap secondhand outboard I was told it was in working order but i have never seen it in action:

1972
Johnson
100hp
Model: 100ESL72R

Installed it all on the boat but the engine will not turn over/crank when i try and start it

First of all i assumed a problem with the amplifer as this has happened to me before on a previous similar engine i own:

1971
Evinrude
100hp
Model: 100193

Both engines are almost identical. The evinrude died a while ago but the amplifier is still good so i swapped over the amplifier and the coil to the Johnson and the engine cranked over fine However it would not fire, spark plugs seemed to be getting fuel so i assumed no spark. I have since found from parts catlogs that the amplifiers on these engines are not the same and this may explain the cranking but no spark perhaps.

See previous posts under 1970's 100hp Johnson and Evinrude compatability (http://forums.iboats.com/showthread.php?t=526071) for more details

i have reinstalled the Johnson amplifier and coil but still no cranking when i'm trying to start the engine??????

I have taken some photos and voltmeter readings below.

Any help would be awesome i'm a little stuck now.....





I have taken voltmeter readings from the wiring loom/harness at the screws number 1-12 left to right with: key turned off / key turned on / key on, fused removed.

1. 0 / 8.5 / 0
2. 0 / 8.5 / 0
3. 0 / 8.5 / 0
4. 0 / 8.5 / 0
5. 0 / 0 / 0
6. 15.1 / 14.6 / 15.2
7. no screw or wire present
8. 0 / 14.3 / 0
9. 0 / 14.4 / 0
10. 0 / 0 / 0
11. 0 / 0 / 0
12.




I'm hoping its not been sold to me with a blown Amp, fingers crossed.

 

[F_R]

Re: Troubleshooting a 1972 Johnson 100hp

Let's stop confusing the issue here. In the first place, that is not an "amplifier", it is a "pulse pack". They are two different systems. Secondly, as I told you in your other thread, the pulse pack has absolutely nothing to do with the starter cranking.

Your voltages appear strange on #1 thru 4. I am having a bit of trouble deciding why. I feel that they should all be zero volts. Perhaps the clipper circuit is blown. However, those first four screws are for the alternator circuit and again have nothing to do with starter cranking. But once you get it running the alternator might not work.

Run some voltage checks where it matters.

1. Test the ground circuit. Place your voltmeter + lead on a good ground on the powerhead, and the - lead on the battery negative post (not the cable, but the battery post). Turn the key to start position. The meter should remain at zero or close to it. If you get a significant voltage, you have a ground problem.

2. Conntect voltmeter + lead to battery positive post, and - lead to the battery side of the starter solenoid. Turn key to start position and voltage should remain at zero or close to it. A significant voltage says a fault in the positive cable.

3. Connect voltmeter - lead to battery - post and + lead to one of the small posts on the solenoid. Turn key to start position. You should get nominal 12V on one small post and zero on the other. If you get zero on both, there is a fault somewhere between the batery and the small posts (including the key switch----OR shift is not in neutral). If you get 12V on both, the throttle is advanced too far or the safety switch is adjusted wrong, or burned up.

If you haven't found the trouble yet, come back for more instructions. I don't feel like typing the entire service manual.

 

[pitprice]

Re: Troubleshooting a 1972 Johnson 100hp

Thanks for the quick response and the wiring diagram, the evinrude service manual one doesn't quite match the wiring i see on the Johnson but thats no suprise i guess.

I have done the test you suggested:

1. 0v

2. 0v

3. 0v on both posts

So it looks there is a fault somewhere between the battery and the small posts (including the key switch----OR shift is not in neutral).

I'll have a look at the remote, key switch and gear shifter see if ican see anything obvious.....

 

[pitprice]

Re: Troubleshooting a 1972 Johnson 100hp

F_R your a legend.

It was something to with the throttle cable/remote i think. Think maybe the new throttle cable was a bit shorter than older one and didn't quite reach comfortably which seemed to be pulling the throttle/ gear lever out a bit. Plus the guy who helped me install engine on the boat connected throttle cable wrongly at the engine end. My fault i should have checked :facepalm:

Remote/throttle is awkward and will not move properly but when its in the right position engine starts and fires up

I think i'll just need to set up throttle cable properly and i'll be away with any luck

 

[F_R]

Re: Troubleshooting a 1972 Johnson 100hp

Simple, huh?