I'll start with the fuel tap: the problem I was talking about would only apply if you were trying to run the engine with the fuel turned off. That isn't going to work, whether the tap leaks or not. Have you checked which position is on and which is off, by disconnecting the fuel hose at the carburetor end, putting the end of the hose in an empty tin, and seeing how fast the fuel flows into the tin? My concern is that you have mistaken the off position for the on position, or the tap is blocked in some way. You need to see fuel running into the tin at a decent rate.
If the fuel tap gasket is conventional (a sort of cardboard-like material, but tougher and fuel-proof) you can buy a piece of it from an auto shop. To cut the internal hole, though, you will need a wad punch of the correct size. You can use snips or scissors to cut around the outside.
I'll give more detail on the ignition timing. First, measure the diameter of the flywheel, and tell me what it is. I'll tell you how far ahead of top dead center, measured in inches or millimetres on the outside of the flywheel, to draw the firing mark. All you need to do is find TDC accurately by putting a pencil through the spark plug hole and turning the flywheel until the pencil has been pushed out through the plug hole as far as possible by the piston (that is TDC). Now leave the flywheel exactly in that position, and make a convenient mark anywhere on the crankcase directly below the outside of the flywheel. Use a square to make a mark directly above it on the outside of the flywheel. When you've done that you can easily find TDC any time you want, just by turning the flywheel until the flywheel mark is directly above the mark on the crankcase. If you do that and tell me the flywheel's outside diameter, I'll explain how to make a firing-point mark.
