70 Johnson Lost Power

[Steele329]

Hi, I need some help on this one. I went out and ran all day Saturday and my 70 ran fine all day. I went back out on sunday and had no issues until out of no where while running at top speed it seemed to gradually slow down but not quite anything too noticeable, just figured it was my imagination. Then when I slowed down to pull up to my favorite beach up spot, it just died. I from there could not get it started for almost a half hour. Once I was able to I had to choke it, then throttle it up to keep it running (in idle.) Once running, i put it into forward and it died again. The only way at this point to get it started was to choke it again even tho it was warm. After a number of tries i was able to get into a low speed and cruise back to the dock. Any attempt to speed up just killed the engine. In the past I knocked the wire off of the top cylinder not the spark plug end but the other end (I honestly dont know what this is called... Any help?) with this condition I assume I was running on two cylinders and the symptoms were similar, but not quite the same. Does this sound like anything anyone has dealt with? Any help is greatly accepted and appreciated. Thank you!

 

[fireman57]

Re: 70 Johnson Lost Power

You could have picked up some crud from your tank and it is clogging some jets in your carb or you could have lost spark to a cylinder. You can check for spark with an old fashioned timing light or a 10 dollar spark tester from autozone. I would check spark first since you have already admitted knocking the wire out of the coil. could be as easy as reseating it.

 

[durban]

Re: 70 Johnson Lost Power

I wouldn't rule out water coming into the exhaust ports

 

[Steele329]

Re: 70 Johnson Lost Power

Thanks can I ask what would cause the water in the exhaust ports? And I checked the wire that was knocked off it looks good, didnt correct the issue but maybe a bad connection???

 

[Daviet]

Re: 70 Johnson Lost Power

You might check your fuel pump operation.

 

[durban]

Re: 70 Johnson Lost Power

the design in the manifold bolting arrangement i found fault with , over the years the manifold tends to warp then water gets in through the gaskets . you may just get away with it by replacing them with 1.5mm novus gasket sheeting make your own , or reface manifold both sides & exhaust box cover the one that goes on top of manifold . ....if this is the problem
http://forums.iboats.com/showthread.php?t=528873

 

[sean mathews]

Re: 70 Johnson Lost Power

a friend of mine had a similar issue. turned out to be sticky choke butterflies. it is even the same year 70 hp johnson.

 

[dodgeboy1979]

Re: 70 Johnson Lost Power

i had a similar problem with my 70, i cleaned the carbs real good and changed the plugs, the motor ran better but not quite right, i noticed my primer bulb would almost go flat at WOT. i think over the years the rubber broke down and the bulb lost its rigidity, i replaced it as well as cleaned the screen on the fuel filter and it runs like a champ now.

 

[fishfeatures]

Re: 70 Johnson Lost Power

i'd check the reed plates at the back of the carbs to make sure one of them aren't cracked.