I've been using the search tool but cannot get clear answers.
73 f250 390 auto. 2wd
Problem that makes me crazy.
Truck was down for a week diagnosing timing problems. Sent it to a mechanic, he found the dist. gear pin was sheared and causing the points to open at different gaps during it's revouluton. He replaced the dist. Truck ran great for the last 3 weeks, better than ever. Suddenly while heading to work it left me stranded. felt as though it ran out of gas. After a few minutes it started but would only stay running with a lot of gas pedal applied. Idleing it would starve out and die. Re started I had to keep left foot on brake and right giving it lots of gas. almost home I slowed down to turn the corner is bogged down, I accelerated and it back fired out of the exhaust twice then shut down and wouldn't start. Pushed it the rest of the way home. New fuel lines from the fuel tanks to the manual fuel valve selector, new fuel line to a new fuel pump. New carburetor put on a month ago. It will run perfectly for a few minutes then sometimes bog down and die and sometimes just shut off instantly. Most everything has been replaced, distributor, plugs, carb, coil, wires are good, fuel pump. Everything except the fuel inlet hoses. Cant tell if they are cracked. Dual tanks, doesn't matter which tank. I have noticed that if I put the manual selector in the off position it does run better while the carb is waiting to run out of fuel from the tanks. Could a manual valve be bad allowing air past that is getting in from somewhere. I am lost and frustrated.

 

If you think the selector valve might be the problem, plumb around it and just run off one tank for a while to check it.
When it does die, does it start right back up or no?
The next time it dies, check for spark right away. Are you still running the stock points and condenser distributor? I know it's new, but the symptoms you describe could be a bad condenser.

 

Years ago a buddy of woke up to find his 69 lincoln was stolen. He got it back and his distributor gear pin was sheared. He replaced distributor, only ran a couple of days and it acted up like yours but died in minutes. Pulled motor, stripped it, the oil pump shaft was twisted, pump was seizing up, cam/dist gear was galling and the pin was sheared again. NOT saying this is the problem and I hope it's not, just your description of the problem brought back the memory. Other contributers are a lot more knowledgeable than me and they will tell us if this is possible. Sorry for the stress test ,I should be wrong based on law of averages.

 

I'd say if it's backfiring it's a timing problem! As the previous poster mentioned the shaft may be twisted which will have shortened it causing it to slip out of your distributor. I'd check that first.

 

thanks all, yes I am still running the stock dist. with points and condenser. I will check for spark next time. It takes a little bit but it will run a few minutes later, and it runs really good. Sometimes it will bog down like running out of gas and then it will also just shut off like the key was turned off. I am baffled. I will change the condenser just because its so cheap and easy. I thought maybe the onetime backfire I had could have been it started to run lean when I was heavy into the gas pedal trying to get it home. It baffles me as to how perfectly is runs for a few minutes then dies.

 

mount a gas pressure gauge in visible location from drivers seat and plumbed right at the carb inlet and drive around and see what's happening.

Did you pull and check the fuel filter?

 

Went and got a new condenser to replace the other new condenser. I used my phone to video myself attempting to start the truck before changing the condenser. Needless to say it would not start. I then switched out the condenser to the newest one, turned the video back on hit the key. Fired right up. I drove around the block and back. Perfect.. Thanks for all of your help. I would have never thought to change it being new and probably less than a couple hundred miles.
If I can figure it out I will post the videos if anyone is interested in seeing the difference.

 

Went and got a new condenser to replace the other new condenser. I used my phone to video myself attempting to start the truck before changing the condenser. Needless to say it would not start. I then switched out the condenser to the newest one, turned the video back on hit the key. Fired right up. I drove around the block and back. Perfect.. Thanks for all of your help. I would have never thought to change it being new and probably less than a couple hundred miles.
If I can figure it out I will post the videos if anyone is interested in seeing the difference.

 

Feels good when you lick a problem doesn't it.

 

A condenser's sole purpose in a distributor is to act like a shock absorber in the ignition.
Electricity has momentum. When the points open, the path of least resistance is to keep flowing across the gap (arcing). This doesn't allow for a sudden voltage drop and the magnetic field in the coil won't collapse so no spark.
The condenser gives the electricity a lower resistance path to follow rather than trying to jump across the point gap.
When you're checking the spark, it should be strong, blue-white and consistent.
When you're cranking the engine over, if the condenser is bad you will have spark but it will be very inconsistent. It will be bright orange then maybe blue-white then back to orange, strong, weak, it will mis-fire, etc.

 

I seem to recall a recent post about a bad run of condensers on the market.

 

Yes Mike, it does feel good. The truck ran so good and smooth this morning that I literally kept thinking that it had died on me again. Wow, the whole distributor was only about 3 weeks old and not a lot of miles on it. I would have never thought of the condenser. Thanks to the advice on this forum I am on the road again. Thanks everyone. I will try to get the two videos on this thread if I can figure out how to do it. You won't believe the difference a condenser can make.

 

Good info Mike. Thanks for sharing.

 

Here's a bit of useless info for you, your condenser is actually a capacitor.

 

Yup, a little storage cell.