Since the the engine has sat unused periodically, it probably needs gaskets, seals and a regulator re-build. Check to see that the check valve is working properly and that the tank is pressurizing. Make sure the plumbing is right. Reversing the fuel/pressure lines will cause this problem.

Contact YS Service at 775-782-4562 and talk with Richard, he will advise what to do and get you the parts you require.