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I am not one to beg for help, but my recently acquired vintage 18 hp, 1969 Evinrude Fastwin is challenging me. When I first took it out on its test run, I ran it about half throttle. It acted like it was hitting dead-heads and eventually popped a pin. After a number of attempts to resolve the problem, I found a used replacement lower unit ( with a prop ) for real cheap. After I put the new lower unit on and fabricated a handful of shere pins out of steel, I never shered another pin. Note: The replacement lower unit was off of a Johnson but it was an identical match to my Evinrude. My only problem is that since I replaced the lower unit there has been a marked reduction in accelleration and top-end speed. The engine is hanging off the back of a shallow hull 14' aluminum boat and used to keep up with a 50 hp Merc. Now it's really doggy. Could this speed reduction be due to an accidental oil/fuel mixture problem? I did have to replace a pin over about thirty feet of open, choppy water and could have upset the mixture settings. It's hard for me to experiment with the mixture setting because when I try to go to the back of the boat and attempt to steer off the tiller I almost do a boat wheely. I know it's not the prop, as both of my props are properly rated and undamaged. Any help or suggestions would be greatly appreciated. Thank you, one and all!!!
You may have a bad seal between the power head and the leg unit. The engine depends on crankcase vacuum on the up-stroke of the pistons to ingest a fresh fuel charge into the crankcase. The seal will leak and actually 'throttle' the engine down in speed. A two cycle is very persnickety about its fuel system.
The seal replacement will require the powerhead to be removed from the cowl and lower unit.
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