'61 Evinrude Lark 3 40HP Refuses to go Fast

[shawnswan]

Hi,
I bought a '61 Evinrude Lark 3 40HP last year. It ran great when we got it, then in the fall it would only go about half speed at full throttle. I changed out one of the coils thinking that was the cause but when I took it out it did the same thing. This year I took the flywheel back off and tested all the connections. One of the spark plug wires was toast so I changed it out. Everything else tested fine. Put it back together and it fired up no problem. It idles and goes slow great but as soon as I start to speed up the engine stalls out.
I pulled the plugs, they're both new. The top plug is covered in oil, the bottom plug is clean. I can start the motor with the bottom plug connected and the top plug not, but I can't do the opposite. The top plug does spark as my body can atest to. I tested it on my meter to.

Anybody have any ideas? I hoping someone will say it's the carb, because that I can fix. I have nothing to test the compression with.

Thanks!

 

[Mas]

Re: '61 Evinrude Lark 3 40HP Refuses to go Fast

If the bottom plug is clean...like new...then water is likely getting into the cylinder and hindering compression while it "steam cleans." Water might come from a failed head gasket or you might have a hole in the exhaust covers or gasket. Can you get a small light into the cylinder and see if the piston is also clean when at the top of its stroke?

mas

 

[samo_ott]

Re: '61 Evinrude Lark 3 40HP Refuses to go Fast

I would borrow or find a compression tester as well as a proper spark tester. Getting zapped just means spark, not a good spark. You need the proper tools to diagnose it. You need to verify the above two items before wasting any more time on it.

 

[F_R]

Re: '61 Evinrude Lark 3 40HP Refuses to go Fast

You say you can start it with the bottom plug connected and top disconnected. That tells us that the bottom cylinder is the one that is firing.

Offhand, I don't remember which cylinder the fuel pump pulse hose goes to. If it goes to the non-firing one, it is possible the pump diaphragm may have a hole in it and flooding the cylinder.

Otherwise, you've got to get a compression reading before going any further. Maybe it's good, and maybe it isn't.

I really don't think it is the carburetor. The carburetor feeds BOTH cylinders. No way can it single out just one.

 

[shawnswan]

Re: '61 Evinrude Lark 3 40HP Refuses to go Fast

Sorry, I forgot to mention when I'm in neutral I can rev the engine high without any stalling.
Not sure if that makes a difference to the diagnosis.

 

[bktheking]

Re: '61 Evinrude Lark 3 40HP Refuses to go Fast

Connect a timing light to the wires and watch the flashing, sounds like intermittant spark.

 

[F_R]

Re: '61 Evinrude Lark 3 40HP Refuses to go Fast

Sorry, I forgot to mention when I'm in neutral I can rev the engine high without any stalling.
Not sure if that makes a difference to the diagnosis.

And don't be revving it up in neutral. Someday you will do that and experience what is called runaway--where it goes berserk and you can't slow it down. Till it scatters its internal parts all over the area. Including some sticking in your hide.