Mid speed range problems?? Evinrude Lark 40 HP '66

[merc20076]

I have an old fiberglass 14' Crestliner boat (restored) with a 1966 Evinrude Lark VIII selectric in very good running condition. It pushes my boat at 29-30 MPH with a 11.5 pitch propeller. But I have a little problem, it's hard to keep a medium speed range like 15-20 mph. It will work well at low and higher speeds. There is a ''dead'' zone playing with the throttle control. In this zone, it will either try to pick up speed slowly to reach finally 2/3 of it's rpm or drop gradually to 1/3 of it's rpm when I pull a notch back at the throttle control.

Could it be a streched cable causing this? Or it's something else? Beside from that it runs A1 for it's age!

 

[merc20076]

Re: Mid speed range problems?? Evinrude Lark 40 HP '66

Any ideas?

 

[Daviet]

Re: Mid speed range problems?? Evinrude Lark 40 HP '66

Can you hear the engine actually change RPM, or is the boat speeding up and slowing down? Thinking there might not be enough power to keep the boat on plane at that throttle setting.

 

[CougarBait]

Re: Mid speed range problems?? Evinrude Lark 40 HP '66

Dont have any ideas, but i can say that my '66 Lark VIII is strong through medium speeds pushing a 15 ft fiberglass runabout. So, i dont think your issue is unique to that motor. WOT i once hit 27.3 on GPS, but 25.5 is my top end.

 

[F_R]

Re: Mid speed range problems?? Evinrude Lark 40 HP '66

The queston was posted last year, so he probably ins't still looking for a reply.

But just in case, it sounds to me like it is a case of coming up out of the "hole". In other words, leveling off into a plane. Once planing, it takes less power to push it.