I am at my wits end on this problem, I have a 1965 F-100 with the 240 six in it with a manual trans. It is original to the truck. My problem is that it will not stay running. I can get it to idle but then after about a minute it dies.


What has been done so far:
Replaced fuel pump, distributor, carb, alternator, battery, distributor cap, plugs, plug wires, spark plugs, points, condenser, rotor, coil.


plug gap and points have been set at settings from manual timing is set at 6 BTDC.


Compression test show to be about 120 psi with only about a 5 psi difference between some cylinders .


It was running fine for several months then it started to hesitate and stall out, thought is may have been the gas. I drained the tank put in octane additive and ran 91 octane with no ethanol in it. Changed plugs out and it ran fine for two days. I then changed out the fuel pump and carb cleaned and checked the plug gaps and points again, truck starts and runs for a couple minutes then starts to hesitate and die. I have to have the idle screw turned up to keep it running at a high idle but then it still will slow down and die. I have exhausted everything I can think of with this.

 

Did you change the fuel filter?

 

Yes, the fuel pump that was on the motor when bought was the incorrect one and was giving too much pressure. It also had a inline filter. I changed that back to the correct fuel pump with the filter as one. It is new as well. Now with the original style pump and filter I get the correct fuel pressure to the carb. Prior to replacing it the motor was running rich.

 

Have you considered the gastank itself? Perhaps it needs to be removed and cleaned. If its the orginal tank its been there for 50 years...

 

I have also tried supplying fuel from a new gas can instead of the tank as I though I may have water in the fuel. It still acts the same, when at normal idle it wants to run really rough and still dies after a minute or so. Almost like the timing is jumping around. would a flat spot on the cam cause that? The biggest thing I think that is beating me up is how it was running so smoothly then the next day I have all these problems, I changed the distributor out and it ran great for a couple days then back to this same issue.

 

I would check that the timing gears have
not slipped at this point.

 

Spark.....


Things that could be bad....first and foremost is the new condenser. They can be bad right out of the box.
Check your connections going all the way back to the switch. Check all your grounds. Intermittent problems are the hardest to find. Heat can expand wire to loose connection where when cold it made a good connection. Check your ballast resistor wire. make sure it's still there and intact.

Fuel.....

Things that could be bad. First and foremost is the tank if the tank was dirty your new carb may need to be taken apart and cleaned. Was there any trash in the lines or the filter? If so some of this may have compromised the new carburetor.

Before I did that I would make sure it was adjusted correctly. It sounds like it's running rich from your description. When it's cold it can run rich, like it does when it's choked but as it warms it loads up and quits. IMHO if it's not the condenser likely it's the carb.

Check all the mounting surfaces to make sure you do not have a vacuum leak. Sometimes vacuum leaks can be found with a propane torch. With the torch on....not lit!....with the engine running pass the torch head over the manifold to head area....if the idle smooths out that's the area of the leak.

Some words on the Loadamatic system Back in the late flathead era Ford got the idea of a total vacuum advancing distributor teamed with a carburetor to work in unison. The carburetor and distributor were matched in the Loadamatic system. Over time it was proven to be troublesome, much more troublesome than a standard points system with mechanical and vacuum advance.
Some literature claims 300s got standard ignition from 65 up while 240s got Loadmatic until 68. In this system the Motorcraft Loadamatic 1 bbl must be used. It is identified by a small round wheel looking vacuum canister on the side. This is the only type of carb that can be used with any real success on a 66 240 with a Loadamtic dizzy. To confirm you have a Loadamatic distributor, if you turn/twist the rotor by hand it should be "springy" with standard dizzy with mechanical advance. It will not spring the Loadamatic system. A later model Carter is not compatible with the Loadamatic dizzy. The Carters are post 67 for the 240 when Ford abandoned the Loadmatic in favor of standard points.

Time........

If you are running.. you should be in time. Now you can be a tooth off one way or the other and still run poorly. IMHO it's unlikely to jump in and out of time. Confirm #1. If the pointer is close but really not right ...you may be a tooth off and will have to reset the distributor.

Sometimes it's not any one problem but a combination of many factors. To get it to run right, you have to correct them all. start with easiest/cheapest and work to the hardest/most expensive.
keep at and be patient...you'll straighten it out.