First, drain the float bowl, as a blob of water can cause this problem, Next, check fuel pump delivery. It should pump with vacuum pulses applied (by mouth) to the vacuum connection. If OK, suspect fuel cut-off solenoid (screwed into bottom of float bowl).
After that, you will have to strip the carb to check for a blocked jet.
phil_saunders(a)bigfoot.com
Phil Saunders
April 2009