Sounds like it may be the accelarator pump on the carbs not pumping fuel.
If you remove the air filters and pump the throttle you should see fuel pumped out from the middle of the carbs. (assuming the float chambers are full). Each choke should do this. This could be the jets blocked.
It may also be the float stuck on one carb.
It could also be ignition related but less likely.(ht leads etc)
Good luck James