1956 Johnson 30hp RD-18 spark

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alwayslearning

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Jun 11, 2007
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Hello all! For some reason I am not able to get spart on the top cylinder of this motor. I replaced the coils/condensors/points/wires on this motor and for some reason am still not able to get spark on the top cylinder. I will be going over all the connections again this week to see if some wire is not connected properly but was wondering if someone could give me a good explanation of what the little diaphram thing does that is connected to the magnito via a small wire. Could this thing be my problem? I know that is not a great discription. I will try to get pictures up here soon.
 
R

R.Johnson

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Re: 1956 Johnson 30hp RD-18 spark

It is called a vacuam cut-out switch. Disconnect the mag. lead going to it, and see what you have. On a mag. of this age, you could have a spark lead breaking down on the under side of the mag. plate, and going to ground. Not uncommon.
 
tashasdaddy

tashasdaddy

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Re: 1956 Johnson 30hp RD-18 spark

i had the same problem with my 58 35 hp. i did not get the plug wire into the coil properly. as said if the cutout is bad it could be grounding the coil. just disconnect on the cutout and give it a try. also check to see it the points slipped and are staying closed.
 
F

F_R

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Re: 1956 Johnson 30hp RD-18 spark

Sometimes even new points have an invisable layer of corrosion on them. Try cleaning them very lightly with some 400 or 600 grit paper. Better yet, if you have an ohmmeter that will read less than one ohm, check the resistance across them. Should be zero ohms with the points closed and more than zero but less than one ohm with points open.
 
A

alwayslearning

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Re: 1956 Johnson 30hp RD-18 spark

Problem solved! I took the mag apart again. Cleaned with acetone, Snipped off 1cm of spark plug wire and reconnected the whole works. Now I have spark on both wires again. Now to put it in the test tank to see if I can get it running. I will have to wait untill I have a burst of energy though. The old beast has quite a lot of compression to pull through! I will have to dig up an old pressure tank for it yet. Anybody have one they want to get rid of?
 
A

alwayslearning

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Jun 11, 2007
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Re: 1956 Johnson 30hp RD-18 spark

Thanks for all your help guys! I borrowed a pressure tank and tested the motor. It fired up and blew all the water out of my test barrel. (Guess I will have to install some baffels). My next project is a 1969 40hp Johnson Electric shift. I love working on these things! It is great to talk over some of the problems I run into, so thanks again for being there.
 
samo_ott

samo_ott

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Jun 18, 2006
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Re: 1956 Johnson 30hp RD-18 spark

Hey AlwaysLearning, I'm in Ottawa also (well actually Chelsea)... I have a few 35's and 40's from the 50's and 60's if you ever want to swap some parts! I also have several of each, 5.5's, 10's and 18's. Steve
 
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