Might pull off the carb and peek at the reed valve.
Well, I haven't worked on one, so I don't know personally. I would suggest going through the carb anyway, it is probably overdue. Diaphrams are likely stiff and not working properly, needle might be a tad leaky, a new kit would likely help.I thought it would be a reed valve engine, but Mike Acres says it is piston ported. http://www.acresinternet.com/cscc.n...0847ffc412ae6e7e88256d0c006b8c60?OpenDocument
If it is a reed valve engine, it would most likely be a broken valve.