72 f250 4x4 2barrel 390. Pertronix distributor/coil.

Truck has run great until a few nights ago. Went to pick up pizza but now idles ok after a laborious warm up (it has been colder). Hesitates on acceleration, low power, pings and low power in 3rd, rarely driveable in 4th. Doesn’t sound the same, engine sounds more rattly especially when cold. Oil pressure / temp normal.

Replaced fuel pump and a short section of tubing to carb that had cracks. Looking into carb, on acceleration drivers side gets a bigger dose of fuel than passenger, which is hardly coming out. Air filter was completely saturated with oil (!) then replaced. Thought maybe old fuel pump diaphragm was letting oil into the fuel. A week ago before this all, drove about 50 miles with choke on, didn’t even notice choke until I got back into town.

Autolite manual choke 2100 professional rebuilt 3 years ago. Vacuum gauge (from lower carb spacer plate for brake booster) reads a bit above 15 at idle, hovers around there when flipping throttle . (harbor freight gauge says late timing at 14-16ish) Had the truck on a dyno last summer and it has run very good, pulling average 12mpg, had 14.4mpg one stretch. Guy at dyno shop put a plug in vacuum advance, I’ve just left it in.

Pulled cyl 1 and 5 plugs and they look fine.(new plugs one year ago with top end rebuild)

timing chain needing replacement or should I go through the carburetor or something else?

I don’t have an uncle bob, so I appreciate any tips if any of this is tell tale of something needing done.

Buttoning up a 4bt, maybe the 390 is getting back at me but needing it as a driver until swap time.
Thanks in advance,
Sam

 

Get a notebook and start a checklist....

1. Check Timing with timing light. 10-12 degrees BTDC is ideal
2. Check for vacuum leaks for WD40 around intake and carburetor
3. Vacuum Advance plugged...wonder why he did that?
4. Check Oil Level...make sure you didn't saturate with fuel when you left the choke on.
5. Maybe before step one...check all cylinders are firing. If necessary, pull each plug, leave plug wire on it, have someone turn engine and with plug pressed against block to verify spark.
6. Fuel Pressure gauge psi?
7. Fuel filter clean?

Been in your shoes, and more than often it's something simple. Lack of Fuel, air, or spark. Good luck!

 

Tough to diagnose anything specific because so much changed.
Eric Hamilton's advice is a good list. I would post this to the FE 390 part of the forum and get their input.

Now if I was to make a solid guess, I would go with timing and fuel. My FE 390 is fuel injected now, but I always had the timing much higher than 10-12. (Edelbrock EFI is at 22 at idle and 36 all in). So I would grab a timing light and rotate the distributor until it idles right by ear, then check how far it is. Unplug the vacuum advance so that it retains the top's end that you are missing. Finally, fuel. It sounds like someone filled it with low octane gas. You can try some octane booster or fill it with higher octane. I throw some race gas in my truck from time to time...smells good.

Good luck

 

If both sides of the carb aren't feeding the same amount of fuel, it needs a rebuild again. Or one of the two jets is plugged by something that made it through the fuel filter. Or came from a dirty fuel filter. When was the last time you changed it? Remove the lid of the carb and inspect the jets. The oil filled air filter sounds like blow by. With the engine idling remove the oil cap with the hose that runs to the air filter. See if there is any pulsing pressure (compression) coming out.

 

Thanks you all for the suggestions. A few days ago I put some gumout additive in a half a tank and yesterday it was back to its old self. So I’m not going to mess with it but I saved suggestions for if/when it happens again. I put some higher octane in and changed the fuel filter.

JEFFFAFA I didn’t notice any positive pressure out the breather tube but maybe a little vacuum. I run a manual choke and set it to spec, but I wonder if driving an hour with the choke on sucked a bunch of oil in.

 

Well that may increase air velocity in the air cleaner, but a genuine Ford oil fill cap does a better job of keeping oil in the valve cover. Plus, that cap and hose are on he air supply side of the PCV system.

 

Thought I’d follow up here, started running rough again and bogging etc. Had my gallon of carb soak ready to plunk it in. Unbolting the carb finding 4 bolts were almost loose. Tightened them up fired it up to see one last time if that would help and blamo, runs better than ever (Tonight at least) took her for a 15 mile drive runs quiet and smooth with power.

Thanks Eric for the tip list and for suggesting vacuum leaks at carb base. I think that was it. Feel sheepish I didn’t check those carb bolts first.

 

stpackard, no worries, glad to help. I get help on this forum all the time, it's a great tool.