First you have to determine if the unit is putting out any spark at all. Pull the plug asnd re-attach it to the wire. Hold it against the head while someone else pedals it. If you are getting spark you can go on.
You say that the flywheel is not marked. OK, first find top dead center. Remove the spark plug and stick a screwdriver in the hole. Rotate the engine until the piston reaches the top. You might have to go back and forth a couple of times until you get it just right. Now mark the flyheel with a magic marker or better yet mark it with a center punch. Mark it in relation to something that you can use as a reference such as a screw or a joint or some such. Then back up the engine about 1/2" on the flywheel and mark this time ith a magic marker.
See if it will run. Squirt a little carb cleaner in the carb. If it goes and then dies, you will have to clean the carb.
Here is an address of a store (Smiths Autocycles) in England that might give you some help. www.autocycles.co.uk