I am resurrecting a late 60s ford F100 that my dad who passed away left behind on our farm. He had the vehicle sitting for at least four or five years and there wasn't much gas in the tank. So after inflating the tiires and towing this to a place I can work I've got the thing cranking, oil level is ok, antifreeze looks good. Truck will run with gas poured directly into the carb and will even run a bit longer with gas poured into the fuel filter bowl with the main gas line disconnected at the pump and a bit more poured down the carb to start. I've used a compressor to blow air through the line and there was a ton of back pressure at the fuel pump end of the line leading to the tank. I didn't put pressure into the line leading from the carb to the fuel pump for fear of popping the old diaphragm. Then I disconneced the rubber line under the driver seat and blew air through the portion between the fuel pump and this location. There's some resistance, but that line seems clear enough that flowing gas should dissolve the remaining deposits. I then tried blowing air from under the driver sear into the tank with the filler cap removed. I get pressure build up in the line at that point and very slow bubbling in the tank sounding something like a bike tube with a few pin holes stuck under the water. I'm thinking at this point there is a layer of sludge at the bottom of the tank that's going to be a pain to deal with. I don't believe there is a bladder in these tanks. Please correct me if I'm wrong. Is there a substance like paint thinner, acetone, carb clearner or whatever that will dissolve the sludge enough to run through the engine to dispose of it? or is this a tank replacement issue? I've put about three or four gallons in the tank, some of which had been sitting in a red plastic can for a few months. I don't want to throw more expensive fuel into the tank until I know it's going to run. Then I can deal with the brake repairs so I can use this truck a bit for dirty odd jobs on the ranch where I'm not worried about gas milage or denting the relatively thin bed of my 03 ranger with a railroad tie. Does anyone have an exploded diagram of the gas tanks on these late 60s trucks? Thanks, edge

 

I had some gunk in my tank on my 70. I ran 2 cans of seafoam through it and it creared a bunch of stuff out.

If yours is that sludgy, I'd probably remove the tank and fuel lines and get some B12 chemtool and soak the parts. you can get the chemtool in spraycans and gallon size cans.