15 hp Johnson with problem

[stienbd]

I have a mid 80s ,15 hp Johnson engine. Have recently replaced the thermostate after noticing poor water flow and engine heating up. Thermostate was seized. The gas I used this year was old and may be heavy mixure. My problem this year is hard to start. When the motor is running I can hear a popping sound(similair to pop corn popping) as I increase the speed and the engine dies as I put it on full throttle. Its like it isn't getting flow of gas. The motor will not stop and still pushes the boat along and doen's seem to be ovewrheating as there is a steady stream of water coming out the water pump exhaust hole. I pulled the plugs and there is a black oil on plug but nothing really bad. Any thoughts would be graetly appreciated. Guy down the road thought maybe a blown head gasket.)[/QUOTE]

 

[Barnacle_Bill]

Re: 15 hp Johnson with problem

First thing to do is get rid of the old gas and see what you have with a fresh tank mixed 50:1.

 

[Xcusme]

Re: 15 hp Johnson with problem

Chances are good that you have a carb problem, if you've had old fuel in the carb bowl. Rebuild the carb, soak in carb cleaner, followed with compressed air. Do a compression test and post the figures here. Compression numbers are relative but both numbers should be within 10% of each other. Do a spark test. While ideling, pull and replace each plug wire. A bad cylinder won't drop RPM's when the wire is removed. If you don't know the last time the water pump impeller was replaced, nows the time to do the job. Don't trust the tell-tale stream of water, if you can place your fingers on the motor head for a few seconds and not get burned, it shouldn't be running too hot. These tests /checks are easy and replacing the water pump is easy with simple tools and a service manual.

 

[wbeaton]

Re: 15 hp Johnson with problem

That's all sound advice. Could be old gas, gummed up carb or ignition.

However, I'd try running on fresh gas before doing anything. As much as I enjoy fixing things I still subscribe to the "if it ain't broke" theory. Except the impeller. That's regular maintenance. Don't wait for it to fail before you fix it. Reading between the lines tells me its time you install a new one.

 

[tashasdaddy]

Re: 15 hp Johnson with problem

totally agree with all said. if you do the carb, don't miss the high speed fixed jet.