Hello,
The problem does not sound like spark problem. It sounds more like a fuel related problem that is fairly common in gensets like yours. The carb is most likely plugged in a jet or passage. These carbs can be cleaned by completely dismanteling all parts and placing parts in an ultrasonic carb tank or something compatible. It is a job for a professional or a strong do-it-yourselfer. For detailed info on exact proceedures of carb removal and cleaning just ask and I would be happy to send more info. It is not usually possible to clean carb well enough when still attached to motor although sometimes you will have have luck.
RVIA Master Certified Technician
Over 15 Years Experience with all brands of RV's. RVIA Master Certified and Trained. Knowledgable!!