1970's 100hp Johnson and Evinrude compatability

pitprice

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Joined
Jan 20, 2010
Messages
23
I have recently brought a second hand Johnson 100hp but i do not know the age or model number.

The welsh plug number is J3686578

I previously had an 1971 Evinrude Starflite 100hp which is almost identical, but unfortunatly it seems to have something terminal wrong with it in the powerhaed and is finished.

The new Johnson is not turning over i suspect the Amplifier/Powerpack is stuffed (this has happed on the Evinrude previously) so i swapped the powerpack and coil from the Evinrude to the Johnson and the motor was turning over fine but not firing. Fuel seemed to be getting to the plugs but i think maybe no spark.

Can anyone tell me if the powerpacks from each can be interchanged do they use the same model?

Evinrude
100hp
1971
model: 100193

Johnson
100hp
19??
model: ??????

Trying to find the source of the no spark problem and the engine will not turn over now with the Evinrude powerpack or the original Johnson one? I suspect i have stuffed the second powerpack as well.......i'm praying not but fear the worse

Any help would be awesome
 

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,195
Re: 1970's 100hp Johnson and Evinrude compatability

Evinrude and Johnson parts are exactly the same except for the hood, assuming they are the same year (and it appears they are).

OK, by not turning over, you mean the starter isn't cranking it, right? The amplifier has absolutely nothing to do with cranking, so you are going down the wrong road there.

HOWEVER, the cranking problem could also be the no spark problem. If there is not enough voltage to crank the motor, there won't be enough to charge the amplifier either. It's like a blown main fuse in your house puts out the refrigerator, plus all the lights and the TV.

The #1 thing you should check for a no cranking problem is the battery. The #2 thing you should check is all the battery cable connections, both ends. Clean them up shiny bright with some sandpaper and make sure everything is tight. If #1 and 2 don't fix it, it is time to get out the multimeter and do some voltage checks. Some electrical knowledge becomes necessary there.
 

pitprice

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Joined
Jan 20, 2010
Messages
23
Re: 1970's 100hp Johnson and Evinrude compatability

Yeah the starter isn't cranking at all now but multimeter readings on battery and the engine are all good!!

Will run you through what i did as its got me confused.

Put new engine on the boat and hooked it all up. Ignition key in the on position mutlimeter readings OK. Turn key to crank it - nothing.

Swapped out the Johnson amplifier and coil for the Evinrude amplifier and coil from my old broken engine as i suspected this could be the issue as its happened to me before. Ignition key in ON position multimeter readings OK. Turn key to crank it - cranks over fine but doesn't fire. Spark plugs appear to be wet with fuel when i removed them to check so i'm assuming no spark not a fuel issue.

Tried checking over connections, had a brief look at the fuel pump, general look around to see if i can see anything obvious. Still not firing then one time when i went to try it. No cranking!!!!

Multimeter readings OK but still will not crank with either old or new amplifer or coil or any combinations of them...

I'm lost now

Will go have a check over battery terminals but think they are OK if meter readings at the engine are good.

I have a basic electrical knowledge so what should i be looking for if #1 and #2 don't fix the problem?

Thanks so much for the quick reply by the way
 

emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Re: 1970's 100hp Johnson and Evinrude compatability

Check the 20 amp glass fuse in the engine wiring harness. When it blows the engine goes completely dead-electrically.
 

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,195
Re: 1970's 100hp Johnson and Evinrude compatability

Well, at least it isn't cranking again, so finding the problem should be a piece of cake. I am late for an appointment, so I don't have time to explain all the tests. Suffice to say that the voltage readings cannot be OK, or it would crank.
 

pitprice

Cadet
Joined
Jan 20, 2010
Messages
23
Re: 1970's 100hp Johnson and Evinrude compatability

Yeah fuse is good i took it out to check and all the multimeter readings on the engine died. Put it back and they are all good again.
 

pitprice

Cadet
Joined
Jan 20, 2010
Messages
23
Re: 1970's 100hp Johnson and Evinrude compatability

I'll take a photo and indicate which of the multimeter readings are good when key is in on position to give you an indication of what i'm dealing with........still have fingers crossed the amplifier isn't blown.
 

pitprice

Cadet
Joined
Jan 20, 2010
Messages
23
Re: 1970's 100hp Johnson and Evinrude compatability

So i think i have found part of the problem, the Johnson motor i have is a 1972 and the dead Evinrude is a 1971. From looking at parts catalogs it looks like the amplifiers on these two are different. This may explain when i installed the Evinrude amp on the Johnson it cranked over but seemed to have no spark.

Evinrude
100hp
1971
model: 100193

Johnson
100hp
1972
model: 100ESL72R

So i have put the Johnson Amp and coil back on the Johnson motor now but it still will not crack over???

I have taken some mutlimeter readings from the engine and have some photos taken but i think i will post them in a new thread as this is perhaps a confusing title now at first glance.

New thread is: Troubleshooting a 1972 Johnson 100hp (http://forums.iboats.com/showthread.php?t=526241)

Thanks for everyones help so far i am getting closer to the problem now i think
 
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