Engine starts easily and very reliable. Made it about 20 years ago. Problem is when it fires it jumps around on the table. My friend made same engine and it just runs along very smoothly. Possibly firing is off?
If timing doesn't solve the hopping, try adding some weight on the flywheel on the side opposite the crank throw. While the flywheel may be balanced, I think the crank puts it out of balance, thus some hop. It's worked for me.
Like all hit and miss engines, if you get it to idle really slowly, it will hop every time it fires. I think that is why so many small hit and miss engines were mounted on a wheeled carriage. When the engine fired, the wheeled carriage would move slightly and then settle back into position.