Johnson 3HP 1968 shutdown mechanism

[ludewig]

Hello,
while rebuilding the ignition system in my 1968 Johnson JH23M 3HP outboard, i wondered how the shutdown mechanism works. There is the throttle lever on the side of the housing, and on the label behind it, it says stop. There is no kill switch. Wonder if it just shuts the carburetor throttle valve so the engine runs out of fuel, or if there is a hidden switch that shorts the ignition system?

Thanks for your answer
Ludwig

 

[seahorse5]

Re: Johnson 3HP 1968 shutdown mechanism

Hello,
while rebuilding the ignition system in my 1968 Johnson JH23M 3HP outboard, i wondered how the shutdown mechanism works. There is the throttle lever on the side of the housing, and on the label behind it, it says stop. There is no kill switch. Wonder if it just shuts the carburetor throttle valve so the engine runs out of fuel, or if there is a hidden switch that shorts the ignition system?

Thanks for your answer
Ludwig

The lever moves the magneto plate which changes timing. The Off position retards the spark too far for the motor to run anymore.

 

[ludewig]

Re: Johnson 3HP 1968 shutdown mechanism

Doesn't this harm the motor over time? Because i'm working a bit with 2cycle moped engines and haven't seen an ignition system which changes timing. Are there any advantages with this system?

Ludwig

 

[nwcove]

Re: Johnson 3HP 1968 shutdown mechanism

no harm to the motor whatsoever.....there are obs almost 100years old that still work fine. the advantage to changing the timing with the throttle is you get good performance from idle through wot. mopeds etc are timed for a sweet spot. ie, if your moped has a clutch, you cant pull away at idle, it will stall. a good running ob will idle in gear all day without a problem.

 

[kfa4303]

Re: Johnson 3HP 1968 shutdown mechanism

+1. Here are some great links that can help explain how it all works and how to keep that little gem running another 50 years. You can get routine parts right here at iboats. Holler if you get stuck.


http://www.duckworksmagazine.com/03/r/columns/max/07/index.htm
http://www.outboard-boat-motor-repa...on 3 HP 1952-1967 Ignition System Tune-up.htm

 

[ludewig]

Re: Johnson 3HP 1968 shutdown mechanism

your replies are awesome
so if i understand this right, could it be harmful to the outboard engine if i would change throttle really fast for a long period of time?
Because, the timing would not adjust in proportion to the rotational speed of the cam because of inertia.
Just my thoughts

Ludwig

 

[nwcove]

Re: Johnson 3HP 1968 shutdown mechanism

your replies are awesome
so if i understand this right, could it be harmful to the outboard engine if i would change throttle really fast for a long period of time?
Because, the timing would not adjust in proportion to the rotational speed of the cam because of inertia.
Just my thoughts

Ludwig

if i understand your question right, its no problem to run an ob at wot all day....if its all set right, and pumping water. not sure about what you mean by "inertia"? the throttle cam only moves when apply throttle , and its all connected to the timing plate. obs cannot be compared to dirt bikes or mopeds as far as timing goes. jmo

 

[kfa4303]

Re: Johnson 3HP 1968 shutdown mechanism

+1. You can run WOT all day, if you want. The timing is "set" mechanically by properly aligning the flywheel on the crankshaft. As you advance the throttle lever, the rate of spark increases by rotating the armature plate of the magneto, along with the fuel/air delivery. Yet another reason folks love OMC (johnson/evinrude) motors of this era. Everything on them is simple and purely mechanical. No fancy electronic ignition gizmos to have fail, or become obsolete.