You have the gearing the wrong way round. You want to gear the engine low so that it more torque. That means that the ratio has to be higher. 4:1 is a pretty high gear ratio. With a 3.5HP engine you are going to have to at least have an 8 or 9:1 ratio. Maybe even lower. This means that the axle...
The keyway on the shaft wont give issues when looking for a clutch. Measure the diameter of the shaft and buy a centrifugal clutch that matches. They pretty much all come with keyways.
You are going to have to gear really low to get any movement out of a 3.5HP engine. Whatever you do, its...
Welcome to the forum. I am from SA too. There should be someone on here that can give you some help. Sometimes it takes a while for everyone to see the new posts :D
I am still around, although not as much as I used to be. I have also tried to get hold of Robert on a few occasions, but haven't been able to. He pays for the server and it is still running :D