My refrigerator trips the GFCI outlet constantly (avg 5 minutes). How do I find an adaptor to run the refrigerator through the L14-30R outlet?

Unfortunately a transfer switch will most likely be needed to power your refrigerator with a portable generator. Since 2014, the National Electrical Code (NEC) requires GFCI's (Ground Fault Circuit Interrupter) on all bonded portable generators for 120V outlets (section 445.20). Since this NEC has, in some way, been adopted into LAW in all 50 states, all of the standards have been updated to include GFCI outlets and follow the latest NEC mandates. Refrigerators tripping the 120V GFCI is not a defect in the generator, the generator is working as designed. It’s the configuration of the electrical wiring in some brands of refrigerators that causes the GFCI to trip. To eliminate any future GFCI tripping, before your next power outage, have a licensed electrician install a manual transfer switch designed to connect to your generators four wire locking plug, to power your house main panel. To locate service centers in your area able to determine the transfer switch that best meets your need, I would recommend visiting Briggs and Strattons website, hovering over the "Owner Help" tab and selecting "Find Local Dealer".