Sir,
If you haven't already, start with a new spark plug and make sure you've got good compression. Check the manual for the compression figures... I believe you can pull the manual down from this site if you don't have one. Next, unless you are a carb guru, have it professionally cleaned. Steve Reed provides that service and uses the ultrasonic bath when he services them. There are so many little channels and things that just cannot sufficiently and the jets can look clean but really may not be. Just some thoughts. Oh, double check that the points aren't burned and that you've got sufficient charge on your battery too... I've learned that lesson myself. There are several things to fettle with on these little bikes and it seems it is usually something quite small but can be tricky to pinpoint. There are folks on this site that are quite knowledgeable (I'm not one of them) so if you just document what you've done, they'll likely chime in with a magic bullet to get you up and running.
Best, Orion
