I have a Sears pressure washer Model 580.761650. It is several years old but has only been used for about 2 or 3 hours and that was recently. It ran out of gas and when trying to restart could not get water to go thru the unit. Let set for a while and water started flowing again. Tried to start and after several pulls the water stopped again. At the same time that the water stops it becomes very diffucult to pull the starter rope. Seems as though it is airlocked but why? Would appreciate any suggestions for a cure. Thank you.