Re: Ted williams 7.5 HP
Hmm...could be a couple of things.
When you have the engine running and you put it in gear, does anything at all happen? Does the engine keep running? If so, pull the prop and check the shear pin. If the shear pin is OK, then you'll need to drop the lower unit and check the driveshaft.
On the other hand, if the engine stops running suddenly when you put it in gear, it could be a damaged gearcase.
Finally, there's a clutch on that engine that is operated by that neutral/forward thing. If it's broken, that will do the same thing.
Give us the model number off that engine, and we'll be able to help more. There's an air-cooled 7.5 built by Eska, and a water-cooled one made by another company.