I have a couple of lifts that do the same thing.What we have found is the pick-up in the tank plugged.Engine runs a while then dies.Starts again then dies.Some mechanics blow thru line but that puts it right back into tank.Tank needs to be cleaned.We also have one that developed a fungus in the tank.That one also needs to be cleaned.We have been fighting that one for 15 years.You can put a suction line into clean fuel in a bucket and see if it works.That can at least eliminate the tank......Hope this helps.