1977 70hp Evinrude

[laramy15]

I have a 1977 model Evinrude 70hp. When I put the boat either in forward or reverse it idles and runs great and does so about 15 mph but when I apply the throttle, the engine boggs down and dies. What would make the engine die under a load? I just bought this motor on an old boat so I don't have any history. Any suggestions would be appreciated. <br />Thanks

 

[JB]

Re: 1977 70hp Evinrude

Howdy, LThompson.<br /><br />I suspect that your engine is idling "great" on two cylinders. <br /><br />Crank it up on the muffs and disable each cylinder in turn by pulling and graounding the plug wires. When killing one cylinder makes no difference in the rpm, you have found a dead cylinder.<br /><br />Check the spark. Needs a hot, blue spark at least 3/8".<br /><br />Got spark on a dead cylinder? spray some fuel mix into that carb. Does the rpm pick up? overhaul that carb.<br /><br />No spark to a dead cylinder? switch coils with a good cylinder. Does the problem follow the coil?<br /><br />Let us know what you find.

 

[BFor321]

Re: 1977 70hp Evinrude

I had the same problem the first time I put my used 1974 70HP in the water.<br />Try blipping the choke when it bogs down.<br />If it comes up to speed for a second, your air/fuel mixture is too lean. <br />My Engine had deposits on the carburator main jets which restricted fuel flow through the jets.<br />My carbs have plugs on the fuel bowls which<br />allowed me to clean them with a toothpick and carb cleaner. A few months later I did a complete tune up and found all three floats levels set differently and the rubber for the fuel pump diaphram was starting to turn brittle and crack.<br />I set the levels and rebuilt the pump for peace of mind. Running lean can destroy cylinders pistons and rings.<br />Also use fresh gas. Stale gas causes my engine to stumble erratically when above idle.