1978 70hp Johnson Seahorse sluggish/stalling

[jculbertson17]

My step-father has a 1978 70hp Johnson Seahorse that is not running right. At first it would be fine and when going full throttle it would run smooth for about 5 min. then it just slows itself down and quits. It took some time to get it started after this. We changed fuel in the tank and tried it again and it started to run well but then we lost power to where we would have it wide open but would only be getting about half the power. Last weekend we couldn't get the thing started at all, it wouldn't even turn over (found out it was just a dead battery) Today though it idled real well and as long as you went slow it would run fine but the second you would push down on the throttle it would just stall. We have changed the spark pluggs in it and checked the fuel filter and it seemed fine. Is there anything else that could be wrong with it? Thanks for your help.

 

[JB]

Re: 1978 70hp Johnson Seahorse sluggish/stalling

Howdy, JCulbertson.<br /><br />Is there a good tell-tale water stream?<br /><br />What happens if you pump the primer bulb when the engine is misbehaving?<br /><br />Have you checked your filter/water seperator?<br /><br />Let us know.

 

[jculbertson17]

Re: 1978 70hp Johnson Seahorse sluggish/stalling

The water pump is running fine since there is a stream of water running out of the hose. We have checked the fuel filter and it looked clean and we even replaced it for good measure. When we prime the bulb it doesn't help any. We are just baffled but someone suggested that there might be a bad coil. Could this be the problem? Thanks for the help.

 

[fireman 757]

Re: 1978 70hp Johnson Seahorse sluggish/stalling

Sounds like you dropped a cylinder. At low speed you won't notice it. Pull the plugs after trying it at high speed. Are they all burning the same or is one wetter than the others. The wet one could easily have a bad or weak ignition coil.