fuel should not be coming out of the vapour hose to the carb unless vacuum is applied to that hose as edward stated. that is a problem that needs to be addressed before proceeding. and i would take his advice on the regulator. fyi the impco model j can be replaced with impco cobra. they seem to be better quality.
i have had to wait overnight once for a flooded engine to clear. funny thing too it was a hyster xm.
if whoever is repairing this is unframillar with lpg systems it might be best to bring in someone licensed to assist.