New Lower Unit Causing Problems

[OldCool]

I have a 1960 Johnson 40 hp. Took it in to have the seals changed and was told it would require a lower unit as the seals have been bad for some time and there was alot of rust inside and other issues. They put in a used, lower unit. I took it out today and before the repair the boat would travel at 20mph. Now after the repair I can barely get 5 mph out of it.

I'm no Einstein but I dont think this is supposed to happen. Does anyone have any ideas of what might be the issue? I would like to go somewhat educated when I try and get the issue resolved with the repair shop.

Thanks in advance for any assistance.

[Paulywood]

I'm far from an expert but if everything else is the same (rpm's) then maybe the gears are wrong? Just an idea.

[GLF]

Like Nick said. Sounds like its the wrong gear ratio.

[2UNREEL]

I highley doubt it is gear ratio. The gear ratio would not make a 75% decrease in wot . I would look to make sure you have not spun a hub in your prop. Also the new (used) lower unit could be cavitating from exhaust around the diameter of the prop housing if it is worn. Does your prop mate up nice and tight? Also due to age of the ouboard you may have an ignition issue with the points. My 2 cents

[Nailer]

40 hp= 2 cylinders? Is it for sure running on both cylinders? If one of the high end jets on the carburetors is plugged, the boat will idle good but run bad at wot (wide open throttle).

I have never herd of different gear ratios on standard outboards. The spun hub could be the culprit. If you have a spun hub, the engine will race at high rpm and the boat will go slow. A spun hub will let the boat move at idle speed like normal.

My guess is the carburetor is plunged.

Buy a can of Seefoam and run it through the engine with a can of gas. That stuff is the best.

[Adam Bomb]

Wouldnt a boat in that year class have shear pins and not a hub? Somethings definitely not right. Make any calls to the people who did the replacement?

[diesel]

the gear ratio only effects the upper gear box i found this out from mercruiser and a murcruiser dealer/repair shop. a good guy to call is miles at d and r sports he might be able to give you a good place to look at for a start

[OldCool]

Wouldnt a boat in that year class have shear pins and not a hub? Somethings definitely not right. Make any calls to the people who did the replacement?

I picked it up Friday after work and put it in the water to test on Saturday around 5 pm so they shop was closed. I'm trying to get as much info as possible before calling first thing Monday morning.