ok i have a 1963 18 horse johnson. It has started running rough and bogging down. It just wont run right and it has like one-third the power it should. I run the mix at 50:1. Is the mix ok? are there any suggestions on what to do to make it run right again.
I would say the mix is okay but anything made before 1964 the book says to mix 24 to 1. You need to do a compression check and a spark test to make sure all cylinders are fireing and compression is good. Anything said before that is done is just pure guessing. If you do a spark test most likely you will find either a plug with a weak spark or no spark. This engine has two sets of points and it uses a J6C champion plug gaped at 30 and if it has anything other then those plugs in it it ain't gonna do right.
The coils were bad about breaking down and giving you a fit to you found it in these motors.They would crack on mine.I have had the 18 Johnson and 25 Evenrude.All had to eventually have the coils replaced.We have a lot of heat under this Georgia Sun.Don't know why,but it was a "THING" with these motors with me.
I have two '58 model 18hp motors. One Johnson and one Evinrude. They are fraternal twins. I had the same problem, and it was trash in the carbureator. Does the engine idle fine? Does it start to accelerate and then die off? These are things that will reveal hints as to the mystery of the ailing motor. As was stated by Pee Wee, the ignition coils can and do go bad. If you have a coil that has broken down, that would be the place to start. Every season, I inspect my coils and change my points and condensers. This is CHEAP :winkreventative maintenance. After checing these items, and cleaning the carb, the next culprit would be the reed valve (hope not):sad2:. Just run the simple tests and let us know what is happening when and if we can help, we will. Good luck.:tounge_out:
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