Haven't posted on the Hamb since 2008 or 2007. Long story short. 59 Ford custom 300 with a 262 truck motor and Holley 1904 single barrel carb. Pretty much the same as a 223, bought the car this way. Had car for 14 years, drove it first 6 years no issues or motor work done to it. Got bored with the scene, kids came, no money, life took over and car sat for 6 years untouched. Got car running last year, new brakes, tires, new radiator, carb, fuel pump, gas tank, plugs, wires, points, condenser, coil, cap and rotor, vacuum advance, new fuel lines from pump to carb. the car ran fine for 11 months until now. And now the the issue. I have a clear fuel filter between the pump and carb that usually stays full. Now it won't fill up. Gets about 1/4 full and you can feel the car kind of starve for gas at higher speeds. Replaced fuel pump and still the same. Blew out original fuel line from tank to pump, air comes out strong at pump end. Tank cleaned out. Tank vent line cleared. Carb has been taken apart and cleaned. If I remove fuel line from carb and start motor, there is a strong and steady flow of gas pumping out from fuel pump. If I hold finger over fuel line at carb when cranking the filter will fill up. But soon as you attach it back to the carb it will not fill up. The car idles fine and revs fine. But when driving at 45 mph you feel it struggle. Can this be vacuum related or can it be internal motor related.
I drive a 223 also. Had several issues but none like you described. Wish I could help. Others will advise better. Good luck.
My best guess, either the fuel pump is losing its prime or you may have something tank related. But a rotted rubber fuel hose could be the problem. I'd check all those first. Did you have the sending unit out of the tank, if so how did the sock (filter) look?
Thanks for the replies and help. Trying to get back in and learn this car after a 6 year lapse. Since the car never had a issue before, this motor stuff is all new to me. Its a new sending unit from Mac's. I don't recall these have a sock filter. It was just the br*** float hanging down. The tank outlet does have a small filter screen in it. The rubber hoses are less than 12 months old and have no sign of cracking. I thinking I might have a small pin hole that is getting air but not leaking gas in the original steel line. That might explain why it pumps gas fine when detached from the carb, but when there is back pressure on it when attached to carb it can't pump strong enough. Also I just checked timing for the first time and I'm not seeing the vacuum advance when revving the motor. Timing is set a 6 degree before TDC where manual says 4 degree TDC. I just left it since car always ran fine before sitting. Not sure how much it's supposed to move but it doenst look like it's moving at all. Could this possibly be some of my problem.
Ohhhh... you got a Custom 300 too.... Your tank is probably okay then. I'd go through the line to look for a leak, if it ****s even a little air that can do it. Replace all the little rubber pieces anyway.
Just had the same problem on another old car. Same scenario. What wound up being the problem for me was the clear filter. It was clogging with something too fine for me to see so I just ***umed it was good. I finally removed the filter element for troubleshooting and the problem cleared up. I don't know if the ethanol is making something microscopic build up on the filter but it looked almost new and perfectly clean. So don't overlook it because it simply looks clean.
Yes, good cheap idea to look at the fuel filter. I never liked those and would never have one over a hot engine. I use those old remote Holley filters that take the Ford fuel pump filter elements (Fram CG20).
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