The good news is that there's not much to the system. With no prime position on the later fuel valves, the system only works with good vacuum. You can simulate that by popping the line off the carb and sucking on it if you're daring. A mityvac would do the trick also. If that doesn't cause fuel to come out, plan to replace the fuel valve. The blessing there is that you can use one from a TW200 which is dirt cheap and doesn't require vacuum. P/n is 23F-24500-20-00, should retail for about $16 plus shipping for a factory (not knock-off) unit.