Out with the fuel, in with the problems
 

I ran my rig out of gas recently, and after refilling it runs awful/barely. Won't rev, no power, very rough and shaky, barely idles and not for long. Choke and throttle don't do much. I took apart the fuel lines and pump-mounted filter, found no crud and even the filter looked ok. Stuck the pump input into a can of fresh gas, confirmed the pump does its job, but no change in running condition. Tried starting fluid, no change.

Poured a little gas down the carb, no change. The last time I tried that technique (on a '78 Datsun with orange goop in its fuel lines), the engine ran great for about 30 seconds before running out of fuel. This one ran the same shade of awful; does that mean the carb is not the problem?

Pulled one spark plug and it's got soot but not an extreme amount. No smoke out the tailpipe. What on earth went wrong? This thing runs like a diesel that ran dry, but it's a 1-barrel-carbed 300 six!

What year is it? I ask because if it has a feedback carb it could have a host of issues not relevant to earlier non-feedback carbed engines.

1973 2-ton truck chassis. Not sure what a feedback carb is exactly, but there is absolutely zero emissions equipment except a charcoal canister that's capped off*. No cat, no EGR. The only two vacuum lines are the brakes and distributor advance. Carb has D0PF-J and Motorcraft on it, references as a Holley 1940.

*I'd like to restore the canister but don't know the correct plumbing. The vent lines from the tanks are hooked up, but the others are the size of heater hoses and are disabled. Modern vehicles would connect it to a purge valve and then the intake, but 1973 medium-duty?

1973? Does the distributor have points? If so, perhaps either the points slipped and closed or the condenser has failed?

Yours is an earlier non-feedback carb and ignition.

Yes, distributor has points. They are not fresh - not much on this truck is - but could running out of gas cause them, or anything else in the ignition, to fail suddenly?

Years ago, while traveling and stopped for a break, I saw a man looking at the engine of his just acquired classic Mustang. He had been driving and hit a hard bump. The engine stumbled and began to run poorly. I asked if I could look at it? I removed the distributor cap and saw that the points were closed even though the block was on the highest point of the lobe. With a screw driver and a credit card, I set the points gap, replaced the distributor cap and the engine started and ran well. The points backing plate must have not have been properly tightened and slipped when the car hit the bump.

Thanks, I'll take a look at them. This is my first vehicle with points, among other firsts. I had the distributor out while replacing the oilpump shortly before the testdrive on which it ran out of gas. Didn't loosen the backing plate but maybe something got bumped.

Perhaps the distributor hold down bolt [clamp] loosened and the distributor moved, throwing the engine's timing off?

Checked out the distributor and did a compression test. All cylinders 155-170, and that's a cold engine with no oil added (oddly enough, they're the same numbers I got last year on a warmed-up engine), so that's not the problem. Coolant and oil look great and there's no smoke, so blown headgasket is ruled out too. Distributor is tight and where I left it. Turned engine over with the cap removed and observed the points opening and closing. They are clearly not fresh, but I don't know what to look for beyond that assessment.

Pending further advice, my inclination at this point is to overhaul the carb and ignition system... and prepare for a mighty scream of WTF?! when it still won't run right after all that :D

Could be the condenser as well. As much as I like the nostalgia of points, it looks like its time for a Pertronix ignitor.

I'll test the condenser when it's less oven-like outside. Meanwhile, doing a lot of reading on ignition and other upgrades for this engine. Won't make a thread until I've done my homework, but I'm all ears about ignition and carb upgrades. Is an MSD coil worthwhile? How about a Carter YF (currently Holley 1940)? Considering anything between fresh stock parts, to a multi-barrel carb and a different coil, to a full EFI swap. Insufficient resources for anything beyond that, like what it really wants: a 1-wire turbodiesel. So I'm looking to improve the basically healthy longblock that's in there now, with priorities of reliability, servicability, economy, and if possible better torque at 2-3k RPM - in that order. It's powering an ~8000lb motorhome, not a racecar or offroader.

That might be the BEST time to test it. Condensers don't like overheating.

Well, the problem is there at ambient temps, so I'll call this result representative: 0.22 or 0.24 microfarads, depending on which range I select on my DMM. Based on this source and others, this condenser tests ok.

The ignition coil reads 8300 ohm secondary and 1.4 ohm primary. Seems ok but that's going off general mechanical knowledge as I can't find Ford-specific specs.

Meanwhile I noticed radial play in the distributor shaft on the order of 0.5mm (20 thou). I can use a dial indicator to get precise numbers. Could this be the problem?

Just took apart the carb and found that the float was stuck down. Seems the black plastic floats rub the sides of the bowl below a certain angle, and running out of gas would certainly explain how it got to that position (though not why it's sticking). But that should cause it to flood, and my symptoms aren't those of flooding, are they?

Ok first post of adding fuel down carb or pumping fresh fuel from a can & starting fluid had no change so thinking not a fuel issue at this time.

I know you took reading on the condenser and said the points look good but I would replace them both along with the 6 spark plugs because of the soot.
Fouled plugs can cause funny things.
BTW what does the cap & rotor look like? Maybe change them and take ohm reading of the plug wires for a full turn up.
Dave ----