How to start 1972 Johnson 4hp?

S__riley

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Aug 5, 2013
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Hi I'm new to this forum. I just received a 1972 4hp Johnson weedless seahorse outboard. The guy I got it from started it quickly with 2 pulls and some messing around with the choke, slow knob and fast knob. Yesterday I hooked it up myself to fuel and it took me forever to get her started. Same again today after I changed impeller, plugs, and lower unit oil. I can get the motor to run but when I start adjusting the knobs I end up accidentally killing it again and I'm back to figuring out where to start the knobs. Is there anyone that can tell me where these knobs need to be for start? And how to put them in a neutral position? Any info would be great!
 

NickMcCabe

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Jul 30, 2013
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Re: How to start 1972 Johnson 4hp?

Keep in mind the guy you bought it from may have warmed it up prior to you getting there, explaining the fast start. To get it running optimally, you first need to make sure the carb is clean, especially the jets. I have a 71' seahorse 4hp and never need to adjust the mixture knobs. At this point you need to get them adjusted correctly then leave them alone unless you are in unusual temperature or altitude conditions. I would try turning the low speed knob to rich, take off the knob and turn the spline shaft all the way. Then use the primer bulb to get pressure in the fuel line and fill the bowl. Apply full choke and it should start easy. Once started, unchoke it and you will need to adjust the low and high speed knobs at low and high rpm, respectively, while under load. Set throttle to low speed and turn the know until you get smooth power with no misfires, then do the same at WOT.
 

S__riley

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Re: How to start 1972 Johnson 4hp?

Thanks for the info nick! I will try those tips tomorrow. It's my first boat engine so I'm learning all these things as I go. I noticed today when using the primer ball I was leaking fuel from the edges of the fuel pump as well. Is this a major issue?
 

Daviet

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Sep 24, 2008
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Re: How to start 1972 Johnson 4hp?

Also make sure to advance the throttle to aleast the start position when starting it cold.
You should not have any leakage at the fuel pump, time to repair or replace.
 

NickMcCabe

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Jul 30, 2013
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Re: How to start 1972 Johnson 4hp?

Thanks for the info nick! I will try those tips tomorrow. It's my first boat engine so I'm learning all these things as I go. I noticed today when using the primer ball I was leaking fuel from the edges of the fuel pump as well. Is this a major issue?

Johnson Fuel Pump Parts for 1972 4hp 4W72S Outboard Motor Buy part #2 and #6 to fix the leak. I'd buy most of the other parts and rebuild it, cheap maintenence while you've got it apart.
 

NickMcCabe

Petty Officer 2nd Class
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Jul 30, 2013
Messages
122
Re: How to start 1972 Johnson 4hp?

Also make sure to advance the throttle to aleast the start position when starting it cold.
You should not have any leakage at the fuel pump, time to repair or replace.

Very important. Put the throttle at START. If it is lower, you will not get fuel (butterfly shutoff is kill switch for these old motors). If it is past START, you will advance the timing too early and it will be sparking before it should be.
 

F_R

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Jul 7, 2006
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28,195
Re: How to start 1972 Johnson 4hp?

Fix or replace the leaking fuel pump

Then put it on a boat, on the lake and start it up and adjust the knobs for best running at high and idle speeds, respectfully. Then forget those knobs and don't be messing with them unless big changes in temp, atmosphere pressure, etc

To start: Tie the boat to the dock (you are inexperienced and don't want to run over something or somebody) Squeeze primer bulb till firm. Give it plenty of throttle, but not wide open. Experience will tell. Pull choke knob full out. Yank the rope. If it starts & dies, push choke in and try again.

Note I said yank the rope. Yes, that is what I meant to say. That would tear up most starters, but this one is different. Just don't yank it all the way out to the end, that will break the rope and destroy the spring. I guess I should say short yank.
 
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