1958 5.5hp johnson RPM problem

[gmarshall43]

I'm working on a 1958 5.5hp johnson. It starts up fine and will run ok for a few minutes but after that it slows down even with the throttle at full. Then it will pick back up to normal RPM and will continue to cycle like that. Sometimes it will stall. I have tried adjusting the low and high speed valves and even replaced the carb with a known good one with same result and the water pump is working. I do get spark on both plugs. Any sugggestions what the problem might be?

thanks

 

[kfa4303]

Re: 1958 5.5hp johnson RPM problem

Hi g. Sounds like you may have one of two issues (spark/fuel). Some electrical components such as the original coils can/do get hot with use and can fail. After the component cools it can then resume function. If this is the case, you may be loosing spark in pone cylinder while underway, thus dropping the rpms and power to approximately half of what it should be. These old motors can start and run surprisingly well on only one cylinder. The telltale sign that there may be an issue are cracked coils and/or dirty points. You'll need to remove the flywheel to visually inspect the various ignition components. Thankfully, new coils, points and condensers are quick, cheap and easy to replace. Coils are about $20 each and a tune up kit is about the same. If the spark is ok, then you proably have a fuel delivery issue. If you are using a 2-line pressure tank go through it and make sure there are no leaks in any of the fuel lines or connections. If your motor is using a fuel pump you can try manually squeezing the primer bulb prior to start. It should get and stay firm. If not you may have an air leak. You can also try squeezing the bulb while underway. If the motor picks up upon squeezing, this also indicates a faulty fuel pump. Give these links a read and try a few of the basic diagnostic procedures and report back.

http://www.marineengine.com/parts/v...ntage-evinrude-johnson/377511/37751100001.htm

http://www.outboard-boat-motor-repa...on 3 HP 1952-1967 Ignition System Tune-up.htm

http://www.duckworksmagazine.com/06/columns/max/index6.htm

 

[jmendoza]

Re: 1958 5.5hp johnson RPM problem

Use a fuel bottle to gravity feed the carb, this will eliminate the fuel pump and tank as possible causes.