Stradicfish40
New member
I purchased a 90hp yamaha ETLD with my 17 whaler. The lower that came with it topped out at 5,500RPM and ran good for a year. When I changed the oil the lower unit had alot of metal on the magnetic plug and in the oil. The spanner nut and hub could not be removed for repair due to corrosion. So I bought a 2nd lower unit from a guy that said it would bolt right on. And it did and runs excellent except only tops out at 4,500-4,800 RPM. I compared both lower units and noticed a few things differtent. (I UPLOADED A PHOTO OF BOTH SIDE BY SIDE ON THIS THREAD). The second lower unit has an extra screw plug next to the " oil level" plug called "wash". The original one does no have that. Also the original lower unit the motor came with have a different angle and shape of the skeg, and the water pick up (vent) on my original lower unit is only 2inches in height and the 2nd is 3 inches. (if that helps at all ) . I have seen both models of lower units on the yamaha 90's. So being crazy I bought a 3rd used lower unit that also runs at about the same as the 2nd. I just want my motor running how it should (topping out at 5,500). MY QUESTION IS: how can I identify what motor the original lower unit came from? becuase its not the origianl of the motor.(it a different shape of blue) Is there different gear ratios?? Have I done somthing to my motor? The compression is perfect on all 3 cyclinders. Im stumped The original gear case is the one on the left. and the 2nd one I bought is the one to the right in the picture.