[Zebu Fellenz]

Hello,

I have a 1961 Evinrude Lark IV with manual shift that is slipping out of gear at higher RPM. It slips out at about 1/2 throttle. When it slips it does not make any sounds (like gear mesh or teeth breaking off a gear) It simply begins to rev up and slow down.

Any Idea's to what may be causing this; I'm pretty good mechanically but don't know much about the inner-working of this motor so please use small words and speak slowly

Thanks,

Erik

[darrklim2]

Sounds like a bad shift dog. IMO

Whats the model #?

[Zebu Fellenz]

Model #35530

Is Replacing a bad shift do a large (expensive) job.

Thanks,

Erik

[BoatBuoy]

Could also be a spun prop, which would much less expensive and intrusive. Do a search for spun prop to get guidance on how to check.

[iwombat]

I agree with the spun prop. Clutch dog feels like hitting a stump.

[Zebu Fellenz]

I'll check for a spun prop and report back.

Thanks for the help,

Erik

[Zebu Fellenz]

I'm Back,

I was at the lake this past weekend to test for a spun prop. For the first half of the trip the boat (motor) ran greatBut after about 20 minutes the problems came back with the boat revving up but not moving at about 1/2 throttle.

I put the marks on the prop and on the hub and after coming out of the lake they were still lined up perfectally.

I believe that this clears the prop as being the problem.

Does anyone know where to look next; the engine is manual shift and when it (slips) I get no grinding or other unusual noises.

If anyone has an exploded diagram of the lower unit it would be greatly appriciated.

Thanks For The Help,

Erik

[F_R]

Does it actually kick the gearshift lever back to neutral? What do you have to do to get it back into gear?

I really don't think it's the dog. But it could be if it's combined with a real loose and sloppy shift linkage. In that case, it would require repair of both problems. A considerable task.

[Zebu Fellenz]

FR,

It does nopt kick the shift lever back at all; it just revs up and begins to slow down. To get the engine back into gear I have to lower the throttle until it starts to run again (usually about 1/2 throttle)

There is no odd noises it just comes back into gear when the throttle is lowered.

Thanks,

Erik

[F_R]

I don't think you have a dog problem. If it isn't the prop, I have to suspect cavitation or ventilation. It's really the same thing, just different causes. It's when air gets around the prop blades.

Is this a boat that you've had awhile and this is something new recently? Do you have floating weeds or grass in your lake? Do you have anything new or unusual on the bottom of your boat? How about marine growth? You would be amazed at what a half dozen barnacles can do.

[ErikF]

F_R,

We have had the boat for a few years, however the motor was a swap and has only been in use for one season (last year). It worked great for the first half of the season and we never had any problems with it. The problems started right out of the blue.

We have weeds in the lake, but if they tangle in the prop we always remove them before we continue on. The prop looks clean and undamaged.

Other than a shift dog are there any other things that could go wrong in the lower unit and cause this problem?

Thanks,

Erik (Zebu) Fellenz

[Evinrude Boater]

It's a 1962 but the gear case should look pretty much like the 1968 Model 40802. You can view the exploded gear case diagrams on the BRP web site. Copy the link without the quotation marks.
"http://12.2.215.22/pub/default.asp?SessionId=f43b6add8cd54164afbf19d3c28b 3510&Lang=EN&brands=EJ,ATV,SEADOO,SKIDOO,SPORTBOAT ,LYNX,ROADSTER"