trouble with 1968 mustang

Replace the filter, check to see if there is any gasoline in the oil. If there is, the fuel pump is leaking gasoline into the crankcase. The next likely suspect place is the carburator.

Of course through the newsgroup it's hard to know what the 'sputter' is like, so an ignition issue might be in play as well.

normally one cleans up the fuel system first if the car has been sitting. siphon all the gasoline out could be mixed with water after sitting, pump out the rest using the starter and the fuel hose off the carb into another hose leading away from the car a ways into another containor (dangerous) this will tell you if gas tank needs replacing too (lots and lots of rusty metal bits). replace fuel filter with a NEW one before driving car plan on rebuild carb with carb kit, your main jet could be gummed up, remember the settings # turns first.

sputter - could also be the distributor cap, arcing on the inside of it, replace it, points, condencer, rotor, usally the coil is ok, but they used to be cheap too. If there is any carbon or dirt inside the cap, it probably needs to be replaced, check with your clean finger.

your fuel lines are probably fine.

You didn't say, but it might be helpful, to know how well the car functions under the 45-50MPH range. For example, how does it start and idle and how does it accelerate before you reach the point it starts to sputter?

For what it's worth, a few years ago I bought a 67 Mustang coupe with a six, that had also sat for a number of years, so I can relate to what your going through. My car had similar problems and eventually I discovered that the cause was no vacuum advance. The car would start and idle ok but at some point while accelerating it would, like yours, start to bog down, sputter and die. Replaced the vacuum advance diaphragm thing that attaches to the distributor and the problem went away. Incidentally, I did add a see through inline gas line filter and it was amazed by the amount of rust that was coming from the gas tank. I did replace the little cartridge in the filter a number of times but eventually the gas cleared up so I did not replace the tank and It has been working fine since.

Gene from Georgia

It's a good idea to put an inline fuel filter before the fuel pump. This way the pump is protected from any crap that might be in the fuel tank.

It's probably the fuel pump. They are cheap and easy to replace. I'de start there.

Don't forget to check for crap in your float bowls! I had a Ranchero with a carter carb that would get clogged with junk that would sneak past the filter. Good luck, Dave

Could just be bad gas. Try adding a small bottle of isopropyl alcohol.

Also, similar symptoms to a bad fuel pump. After a while, the rubber diaphragm in the pump dries up and volume and pressure drop as the rpm's climb.