Did you completely drain the fuel tank by removing it from the motorcycle, then add fresh fuel & drain that?
Did you drain the carburetors & drain fresh fuel thru them as a rinse?
This is battery season: have you checked the battery with a digital multimeter & done a load test? Was the battery properly serviced & checked before installation, and maintained with a good motorcycle smart charger.
Even if a battery is new or fairly new, test it. Never assume a battery is good.
1981 KZ650-CSR. Competition, Sports & Road.