I've got a 1977 620 with 29,000 orig. miles that has been garaged since 1994 and want to put it back on the road. This is whats been done so far, new carb, electronic distributor, new battery, new plugs & wires, new fuel pump, new exhaust, flushed and changed fluids, new master cylinder and wheel cylinders. Haven't replaced belts & hoses yet... now the problem. Keeps running out of fuel and the tank is half full. I flushed out the tank and installed a new fuel filter. If I prime the carb it will start and fill the carb and run for awhile but slowly lets the carb go dry. I placed an electric fuel pump ahead of the mechinal one and kept it running for awhile. I think the pumps are sucking air somehow maybe a hose at the tank ? There isn't any sign of a leak. I saw in a manual that there is a small reserve tank ahead of the main tank ? Is anyone familiar with this system or what other problem it may be ? It looks like the gas from the tank is running up to the carb and returns back to the tank. Does the fuel run continuly, in a closed system ? Can the gas tank cap effect the delivery ? I'd appreciate any advise on this fuel problem.

If you fill the tank up will it stay running? How much fuel was in the tank when it was in storage? I saw this problem on a friend's 810 that sat for 15 years with 1/2 tank of gas. Turned out that the steel pickup line inside the tank was perforated below the level of the gas that was in the tank, which after 15 years was basically varnish anyways. Got another tank from a junkyard and all was well. Chris.

One thing nice about these trucks is they have a drain plug in the gas tank I have an electric pump on mine and kept having issues and thought I was burning through pumps it turns out the connector in the cab where the wiring ran out to the pump was bad so I ran a new wire and its been all good since. I would drain the tank blow out the lines and 86 the manual fuel pump and run an electric.