Hey guys,

This past saturday we headed out and almost immediately had some knocking and hesitation when accelerating. We couldn't get the boat to do more than 25mph with out it knocking really hard. The boat would idle just fine but as soon as you got her above 15mph or so she would start hesitating and knocking again. We got home and checked the wires, cables and idle. That all seemed to check out ok. So we took her to mechanic and he's telling us that the timing is off and the prop hub is slipping. Apparently the knocking is most likely coming from the prop slipping.

Being a novice, that sounds like an honest assessment but i'm not sure.

The prop on this motor is very old, warped/bent a little and has a few knicks in it so i'm not surprised if its causing an issue. But does the timing on an outboard normally need to be adjusted, is this common?
Its a 91 Force120.
Thanks in advance for any input/advice.

Be sure to have him check the flywheel key,it may be sheared off.You wont get a knock from a spun hub,all it will do is rev up and not go anywere,souinds like you have lower unit damage and may have sheared your flywheel keyway.

i agree with limit5.

a spun hub will just over rev. the engine. the bent blades will make the engine vibrate, but won't knock. if the prop is severly bent and vibrating badly, it will eventually wear out a lower unit. that is possibly where the knock is at????

replace the prop with a new one and run it again if you want.

pull the bottom plug on the lower unit and see if there is any metal in the oil, big chunks are not good.

Is it a slap or a knock sound? Slap is usually in the power head.
Deeper sounding knock is lower unit, usually.

If it sounds like it's coming from the lower unit, I'm guessing worn dogs on the gear set. but just a guess. Like they said....borrow another prop and try it. If it still does it, drain the lower unit oil and look for metal.