1977 Evinrude 70 HP 70773S

by Robert Buchanan
(Pearland Texas USA)

This old barn find engine is in near mint condition. It had set for maybe twenty years in a garage on a 16'VIP tri hull. I bought the boat two years ago and found the engine slightly seized. With some coaxing and PB Blaster, I made it run on a Seafoam and fuel/oil fresh mix and new plugs. Immediately thereafter, I rebuilt the carbs and changed a few hoses. New impeller, checked fluids and changed. A good overall seasonal ready for the water. Took it to the lake and ran it through thirty gallons of fuel, pulling floats with grandkids, and in general have a blast with this fast and maneuverable craft. It purred like a new motor all summer and into fall (Texas). It sat for the winter last. I found the fuel pump intake cover to be cracked ( I assumed from age) and replaced the whole fuel pump, did a quick update on the carbs. Started fine (very easily, just a couple of bumps on the key) and ran up to 3500 RPM and then bogged down. Up to 2000 RPM runs fine. I suspected the new (not OEM) pump. So when a buddy ran the boat I sat behind and pumped the fuel bulb. Sure enough...the boat sprang to life and ran up to 5800 maybe near 6000 and ran like new when manually feeding the motor fuel. I checked the fuel pump output and it seems to be fine. Lots of fuel output. Tried again the following morning and when cold she ran up to 4500 RPM and remained steady for maybe one full minute.I throttled back to idle...and then romped on it. Wound up great to 3500 or 4000 then fell on her face. Idled back to dock at 2000 to 2500 okay. Stumped on this one. Before I make an expensive mistake with parts I want some professional input. I am somewhat mechanical and have some basic test equipment. When cold or warm, just a squirt of choke and a bump of the key and she starts. Idle is a little bumpy but solid. I have an Evinrude manual and a basic flowchart for the troubleshooting.

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