Topic: ‘55 Johnson 3 hp won’t fire – Antique Outboard Motor Club,Inc

This topic has 28 replies, 12 voices, and was last updated 1 month, 1 week ago by fleetwin.

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May 21, 2025 at 1:47 pm #296594
Dennis Drake
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US Member
I need help figuring out why I can’t get my 1955 Johnson 3 hp started. In fact, it won’t even fire once.

I’ve rebuild the magneto and carburetor. And I’ve determined neither is causing the issue. I have another 1950’s Johnson 3 hp that I’ve restored. It starts and runs perfectly. So I put the magneto and carburetor from the smooth running engine on the problem engine. It still won’t fire.

I’ve checked the compression on both engines and it’s a close match – around 60 psi in both cylinders on both engines.

I’ve checked the condition of the reed valves and they look fine.

I’ve put a new head gasket on.

I’ve pulled the plugs after trying numerous times to get the engine started, and the plugs are bone dry. For some reason, fuel from the carburetor is just not being pulled into the cylinders.

Any suggestions on where I should look next?
May 21, 2025 at 1:51 pm #296595
RICHARD A. WHITE
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Lifetime Member
When you say you “rebuilt” the carb, please let us know what you did for the “rebuild”.

With dry plugs, that does tend to lead one to the carb, so clearly the fuel is not getting thru the carb, so I would surmise it has plugged ports and such.

Did you use an ultrasonic cleaner to thoroughly clean the carb? Did you remove all welch plugs to ensure there is zero blockages?

Richard

http://www.richardsoutboardtools.com
classicomctools@gmail.com

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Dennis Drake
May 21, 2025 at 2:33 pm #296596
Gary Haight
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US Member
To see if it is a fuel issue, remove the spark plugs and squirt a TINY bit of fuel mix in cylinders. Reinstall spark plugs and try to start engine. If it fires, you know it is a fuel issue.
Maybe a possibility but did you check the crankcase seal or seals to see if they are good? If they are bad, it may not create suction through carburetor pulling fuel into crankcase.
May 21, 2025 at 5:10 pm #296600
seakaye12
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US Member
Has the crankcase been split? If so maybe the joint has not been sealed properly and is allowing loss of crankcase pressure/vacuum?

Those engines have no crankshaft seals but could loose vacuum at the joint.
May 21, 2025 at 5:20 pm #296601
crosbyman
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Canada Member
when you say won’t fire….. do you mean will not generate SPARKS or simply will not ignite fuel

crankcase vacum leak aside the carbs are easy to service and to start a critical area to check is the very narrow side channel that routes fuel from the bowl to the chamber under the welch plug. make certain the idle screwpoint has not snapped off and blocks fuel circulation

Shot for fuel in the carb face will confirm the carb is NOT passing fuel up the side channel anddown the 3 small holes under the welch plug

https://www.youtube.com/watch?v=MfTpU6HS4cA

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May 21, 2025 at 5:39 pm #296605
bkrsdoz
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US Member
I assume that you replaced the could and condensers, and cleaned the points. Did you check for spark on both cylinders? If you remove the air silencer and spray some mixed fuel into the carb air inlet and pull the start cord, does it fire?
May 22, 2025 at 7:42 am #296618
Matthew Pieklik
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US Member
points wired to the correct coil?
May 22, 2025 at 8:57 am #296620
crosbyman
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Canada Member
reread your top post !! … mag and carb from known good 3hp did not change things.. bit weird I admit

Front coil wire to top plug ok ? per Matthew’S suggestion !

do you or not have sparks … can you feel a good suction on the from of the carb face ?? does the carb fill up or tank filter plugged ?

tank valve open ?? ( had to ask)

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May 22, 2025 at 9:10 am #296623
Dennis Drake
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US Member
Thanks to everyone that responded to my post. Regarding all of the questions about what I did to rebuild the carb and magneto, yes, I did all of the suggested items. And I determined neither is the culprit (as I stated in my original post) as I swapped out both the carb and magneto from a working engine, with no change – still wouldn’t fire.

And when I put the carb and magneto from the non running engine, on the working engine, it still started and ran just fine. While I appreciate the suggestions, the carb and magneto are NOT the problem.

As to other questions, yes, I did try spraying fuel into the throat of the carb. It still did not fire. By that I mean there was no audible “pop” from combustion in the engine.

Yes, I did try removing the plugs, then quickly reinstalling them after spraying fuel directly in the cylinders. Then there was an audible pop (i.e. it fired).

I think the response from seakeye12 is the most on target to solving my problem. I will definitely check all the crankcase seals for a possible leak. Again, thanks to everyone.
May 22, 2025 at 9:12 am #296624
Tubs
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A "Boathouse Repair" is one that done without having tools or the skills to do it properly.
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