1979 85 HP Johnson V4 blows fuses

[andreipou]

Hello,
I took my boat to the lake today first time after the winter.
Before that I started motor (85ML79R) with muffs and it ran fine.
Spent a few hours on the lake and it worked fine.
I was getting 30 mph max instead of 34 mph as last season, so I decided to run it again when I got back home to check timing and carb adjustments.
It did not start.
Fuse blown. I put another one it blew right away, then another one.
I ran out of those tiny fuses.

Can anyone give me idea where to look, not sure what could happen during drive home.
Wires look fine.

Thanks.

 

[jimmbo]

Does it blow as soon as you insert it, or does it wait till you turn the key to on? That fuse is the Feed that goes up to the Control. I suspect a pinched wire, or a short to ground, perhaps even the Key Switch itself. Being 44 yrs old, it may have broke

 

[Crosbyman]

the fuse fed of the solenid sends power to the switch via a connector ... in 1980 anyway...

check all wiring for chaffing- grounding

if it blows on choking only then the choke solenoid or distribution to it is grounded.
if it blows onstarting only then the start solenoid or distribution to it is grounded.
your key switch may also have an internal breakdown and blows the fuse

as ex: see the 1980 diagram from https://maxrules.com/graphics/omc/wiring/80_81_V4.jpg

it may help

when you KEY ON any accesory fed +12v can cause a blown fuse.

 

[jimmbo]

That is an diagram for 1980, a 79 could be different in several Areas.

 

[Crosbyman]

yes I am certain it is.....but basically even with some difference the testing process will be the same.

the 73-76 version is very similar distribution and switch wise

solenoid....post source of +12 to fuse... then to switch.... to power distribution to ...start solenoid, choke, accessories etc....

fast blowing fuses usually have a short to ground somewhere. ....
blowing at START or CHOKE narrows it down


universal process of elimination ...remove loads and reconnect gradually till it blows

 

[andreipou]

Does it blow as soon as you insert it, or does it wait till you turn the key to on? That fuse is the Feed that goes up to the Control. I suspect a pinched wire, or a short to ground, perhaps even the Key Switch itself. Being 44 yrs old, it may have broke

It happens when you turn the key

 

[andreipou]

I have exactly the same RC from spare 50HP, so I will disconnect it at the red plug and reconnect just a new RC plug to make sure short is not on the engine itself.
Then I will try to see if it CHOKE or START that blows it.
Then I can even swap the switches (I have a wild guess that it will be a switch).
That is the plan for now.
Thanks for the help.

 

[andreipou]

I was down sick for a while and now got back to this problem.
I disconnected red plug and connected spare RC.
Fuse blew after a few starts, so it was not a key switch.
By playing with it I found that pushing in for choke causes the fuse to blow.
I removed choke solenoid and connected voltmeter.
It was starting fine, fuse was fine, and voltmeter was showing 12V when key was pushed in for choke.
Then I applied 12V to choke solenoid contacts and it was working fine "sucking in" rod as intended.
Puzzled, I reassembled everything, and it worked fine from that point. Fuse was fine, engine runs fine, choke works fine.
Do not know what the problem was what is a bad thing because it means that it can come back when you expect it the least...

 

[oldboat1]

Wire brush the battery terminals and the leads until bright and shiny (sandpaper probably better on the leads). Make sure the polarity is correct when reconnecting, and tighten down with a wrench (i.e., hand tightening is not enough).