I have a short shaft, 1987 Evinrude, 4hp Outboard Motor, Model Number #E4RCUD, Serial Number #B 1373608. I am using this outboard on a very light weight 13ft. aluminum boat. The motor & prop have never hit any underwater obstacles or been run thru the mud or sandy bottom.
My outboard has a 1987 (vintage) OEM Factory 3-Bladed Plastic Prop is a (P/n #0319774) which has a 7 1/2 Inch Outside Diameter and a 7 Inch Pitch. At engine speeds up to 1/2 Throttle, the propeller bites in to the water nicely and powers the boat right along at trolling speeds. Anything above 1/2 Throttle the engine RPMs rev up suddenly and the boat seams to slow down. If I lower the engine RPM back down below 1/2 Throttle, the propeller bites in again and seams to power the boat right along at trolling speeds. With the outboard secured to the boat’s transom, the cavitation plate appears to be located 3 to 4 inches below the surface of the water.
I took the Prop off the outboard, and carefully removed the Rubber Prop Clutch Ring from the interior of the Propeller.
I then visually inspected the interior and exterior surfaces of the Rubber Prop Clutch Ring. There appears to be some visible signs of rubbing marks (or slippage) on the splines located on the exterior diameter of the Clutch Ring. The splines located on the inside diameter of the Clutch Ring might also have some minor visible signs of rubbing, but it is difficult to see the interior surface of the Clutch Ring very well. I also visually inspected the Prop Clutch Hub (P/n 0398316) and there is are no signs of rubbing or ware marks on the splines located on the exterior diameter of the Clutch Hub.
From Evinrude, I just purchased a brand new Rubber Prop Clutch Ring (P/n #0310331) and pressed it into the interior of my original Prop. The new Clutch Ring fit very tightly into my original Prop and took some serious effort to press it down into the splines located inside the Plastic Prop.
I then reinstalled the Prop onto my outboard and took it for a test ride. Again at engine speeds up to 1/2 Throttle, the Propeller seams to bite in nicely and powers the boat right along at trolling speeds. I slowly increased the Throttle and made it to about ¾ Throttle and then the engine RPMs rev’d up suddenly and the boat seamed to slow down again. I lowered the engine RPM back down below 1/2 Throttle and the propeller bit back in again and powered the boat right along at trolling speeds.
I then took the Prop off the outboard and turned the Engine’s Output Shaft by hand and I could feel the engine’s pistons generating compression in the cylinders. I’m not sure if there is a coupling located between the base of the Motor and the drive shaft but there doesn’t appear to be any slippage.
I’m at a bit of a loss as to how to proceed. Any advice you can provide would be hugely appreciated.
You already asked this same question in the Evinrude Pro's forum but we will copy the link to the answer here for you.
"There is never just one thing wrong with a boat";
-- Travis McGee, main character in a book series by John D. McDonald
The factory recommends that a properly trained technician service your Johnson or Evinrude outboard motor. Should you elect to perform repairs yourself, use caution, common sense, and observe safety procedures in the vicinity of flammable liquids, around moving parts, near high-temperature components, and working with electrical or ignition systems.
The information offered here is only general in nature and should not be construed as complete factory approved procedures, techniques, or specifications. Always use the proper service manual for your motor, up-to-date service literature, the correct tools, and have an understanding of how to proceed with troubleshooting and repair methods. If you are unsure or uncomfortable with a procedure, a situation, or a technique, enlist the services of a factory trained technician.