Weird problem with my '57 Fastwin

[Fastwin]

So here's what's going on. The motor idles rough, gets to 3/4 throttle then revs out like there is air getting to the prop - but there's nothing under the boat or on the motor. This has happened the last 3 times i've launched the boat.

Could it be a compression problem? Are you confused? I bet you are, that's why I have added the following video to YouTube describing the problem as it is happening:

http://www.youtube.com/watch?v=G08jCBchROE

 

[bigsack]

just a shot in the dark, but is your hub slipping?

 

[EricM]

It does seem like the prop hub is slipping under heavy load. Have a prop shop look at it. I don't think the rough idle is related. Good luck and let us know!

 

[buzz]

I think spun hub also. Not running....in gear, turn prop with your hand and see if you can detect any slippage. You may have to hold the flywheel nut with a wrench, to keep it from turning. Rough idle usually equates to bad gas/fouled plugs/etc. These old motors are tough little warriors.

 

[Bubbakat]

shear pin may be to short or the rubber in the hub is deteriorated. The rough idle could be from a slightly foulded plug. Put a champion j6 or j4 plug in it. They don't run real well on other plugs. I thing I may have a motor in my barn like that one. If you need it for parts sing out. you can have it.

 

[Fastwin]

Yeah man! That would be cool. When could I come look at it?

 

[Fastwin]

I think it is a spun hub after all the reading many replies here and on iBoats.com I bought a new prop so we shall see! Thank you for all the help guys!