Do a compression test 1st,if that's ok,check for 4sparks off all leads,if that's ok.get some easy start and spray around that inlet area to see if its sucking in air from somewhere(while the engines running)(revs will rise if air leak)service the carbs and balance them,check ALL the fuel pipes for blockages and drain the tank/check flow from outlet.
Where you too fella?
Where you too fella?