TOPIC: '66 40hp evinrude selectric slipping at full throt

L/U ok at low to midrange speed. Gradual increase of throttle to higher speed results in engine suddenly revving to high speed and thrust slacks off. Reducing throttle results in the thrust and engine speed returning to normal. The prop hub does not slip when turned by hand, I can feel the compression on the cylinders. (the prop hub was a problem last time out...) Could this is the spring/gear engagement being worn, like the mechanical shift dogs and gear do? If so, do both gear and spring need replacement, or maybe just do both as long as it is disassembled? Is reverse not far behind in wearing out? Also, voltage to the coil is 10.5V, so I cleaned up many connections, however the knife connectors under the cowl are still original. There was some white metal filings in the gear oil when I changed it in spring, as well as some water, so I rinsed the housing with mineral spirits, let it dry, replaced the prop shaft seal and bearing, and filled with C type fluid. The drive shaft seal was replaced when I changed the impeller. Any thoughts or input would be appreciated.

Of course it could be the clutch spring and hub. Or low voltage. However, don't just assume the worst before checking the prop hub. It is easy to check, but can't be done by turning it by hand unless you are stronger than 40 horses. To check, scribe a line on the plastic prop nut and another line on the propeller, aligned with the first line. Run motor until suspected slippage occurs. Stop motor and check your lines. If they are no longer aligned, the hub slipped. Replace prop or have it re-hubbed.

And check that low voltage. That can make the spring clutch slip and wear.

ok, got it, makes sense. I will check it out. Thanks!

Ok, so I marked the prop, and after slippage occurred, the marks were still aligned. I have full battery voltage at the switch terminals, but only 10.5V at the knife connector under the cowl. The engine was home to some mice before I owned it, so there could be some corrosion at the crimps for those connectors, although they were covered with their rubber sleeves. I'll slit the insulation with a razor and check the voltage before the connector. I have had wire go bad on other projects, and fixed the trailer lights problem by running a ground wire direct to the bulb sockets, so maybe new wire is in order...

Let me ask you a question on your troubleshooting.
Are you checking the voltage with the engine not running and in gear? Am thinking you are.
What is battery voltage at the battery terminals on the battery. Check both in gear and out.
Secondly, I take it you have a functioning generator on this engine so start the engine and check at 2-3000 RPM in neutral and again in gear.
I agree with what you are doing in checking the wire and terminals on the shift wires but this would be good to know as well.
You may find that you already have sufficient voltage at higher RPM. Good check to make.

The battery voltage does not increase with the engine running, in or out of gear. While running on the lake the voltage holds 12.3V This indicated the generator circuit was not functioning, and from the testing, and recent polarizing of the generator(motor test works) it looked like the regulator was faulty. However, I checked the junction box fuse and found no continuity between the clips. The fuse was good but 55 yrs of corrosion needed to be removed. So I need to go back to the lake to test that. But the new wiring is delivering those 12V to the shift coils, much better than the 8V(rev) and 10V(fwd) before. Running at the improved voltage however did not correct the slipping from occurring with throttle above moderate speed. Slower speed, its not slipping, and no slipping in reverse. So, does this indicate the hub needs to be replaced? and the spring? Or perhaps a weak coil? The repair manual says they should be aprox 8 ohms. They are 7.2(F) and 7.8(R)

Trying out the improved continuity at the fuse still did not result in generator output to the battery. Grounding the field which is supposed to bypass the regulator did not show any voltage either. So the regulator must be shot. Any advice on a replacement part? There are a few used ones on ebay... 15V, 10A.

Sounds like you are on the right track. You need one, no ifs ands or buts when you have an electric shift.

Ok, I bench tested the gen using a hand drill, there was 2 volts. That will be better with higher rpm from the engine. After reading the Clymer shop manual again, They mention that only a slight ammeter needle movement would result if the battery is fully charged. Perhaps the regulator is not "turning on" with a battery that is above 12V? I'll put it back together and try again with a run down battery... The ammeter does show discharge when running the starter. Any thoughts?

usually after starting you should see negative needle movement. Turn on your running lights and that should show a negative needle movement that should correct if the generator kicks in.