1977 25 hp johnson outboard

[keetamae]

I have a question to anyone who can help .. I have a 1977 25 hp. johnson outboard. when it is cold it runs exc. but as soon as it warms up one cylinder is breaking down and it ships.... But then if you first start it and run it like I said it runs great till it warms up... Please help !! think it is a coil??

 

[Chriswalden]

Re: 1977 25 hp johnson outboard

Sounds like an ignition problem to me, probably your power pack. If you do not already have an inline bulb spark tester, you can purchase one from just about any auto parts store. Plug that one into whatever cylinder you suspect is "breaking down" and run it until your problem occurs. That will tell you if it is an ignition problem. It could also be a host of other things. Just do a little troubleshooting and post your update. Hopefully you are running it with a water supply to the pump, i.e. water clamp or a barrel or maybe even in the water. If not you could be overheating the engine and that is causing the problem. Its probably a dumb question to ask but you just never know.
Edited Post.

 

[eavega]

Re: 1977 25 hp johnson outboard

Most likely suspect would be a bad coil. It works just fine until the motor warms up, then the heat causes metal to expand, and something is shorting out. Break out a spark tester and check spark when the motor warms up. I'll bet you won't see a spark. Even better, try to run it at night in the dark. You might see where the ignition system may be arcing out.

Other things to check would be that your tank is properly vented, fuel pump is pumping fuel (although that would cause the engine to stop, not to drop a cylinder.

Rgds

 

[Chriswalden]

Re: 1977 25 hp johnson outboard

You haven't posted back in a while, I am curious to know if you found the problem?

 

[keetamae]

Re: 1977 25 hp johnson outboard

I want to thank you for your input. We haven't done anything yet. We have to wait till we can take it to the lake this spring. My husband did put in a new coil.. But to see if that was the problem we will have to wait and see.. as soon as we can get it in the water we will know more... thanks !