My timing light doesn't flash when the mark is at this setting. It only flashes when I turn distributor clockwise, then truck dies.

 

Many Fords have damper or vibration absorbers notorious for slipped outer rings. It sort of "sounds" like this is what you are describing. The cast part and steel outer ring have a rubber sandwich in between them that allows the outer weight part to twist or "lead and lag" the crankshaft as it spins and absorb torsional vibrations. But the rubber has all rotted by now and the bond breaks. This makes the timing marks completely inaccurate. Also a risk of the damper weight launching itself through something important and the crankshaft cracking or even breaking. Not saying this is your problem but it 's something to look st depending.

Anyhoo when ya get the #1 piston to a known TDC on the compression stroke, the rotor should point to the #1 terminal on the cap, and the balancer pointer should be on the "0" mark. If not, then something is out.

 

Turning the distributor clockwise is advancing the timing, counter clockwise retards it.

The light should flash no matter what number the balancer is set at...that means #1 cylinder is firing and gives you an idea of where the timing is set - 8,10,12 degrees BTDC. You are hooked up to #1 plug wire, yes?

You don't need to turn it much - can you see the numbers on the balancer? What numbers are showing when it flashes?

 

If the balancer has slipped as Tedster9 suggests, there are a couple options open for you. Some people time their engine with a vacuum gauge - advance or retard the distributor until you get the highest vacuum reading then back it off an inch of Hg or so. Vacuum gauge should be hooked up to manifold vacuum.

Another way is to get or make a piston stop and get some timing tape. Affirm you're at 0* TDC with the piston stop and attach the tape such that the pointer is at 0 on the tape.

 

Number 1 piston is up. Rotor button is at number one plug wire in distributor. Timing mark is at 10.

 

Timing light only flashes intermittently. Not all the time. I am hooked to number one plug wire.

 

Timing lights can go bad...how old is it? Can you check it with a known good engine?

Have you ohmed out your plug wires?

 

Well it's supposed to flash intermittently. Sorry..

No, like Mr. Filthy B. sez, for now you can set timing with a vacuum gauge connected to manifold vacuum. Some people can time OK by "ear" or "power time". Here's how to use a gauge.

Disconnect and plug vacuum advance, set idle to around 550 or 600, as you advance distributor (clockwise) the idle RPM and engine vacuum on gauge will increase. As you continue advancing, the timing gauge needle will top out and flutter, and the engine idle will start to wander or "hunt". Too far.

Usually a healthy stock V8 will pull a nice rock steady 18" or 20" maximum at Sea level. Back off slightly from whatever the highest _steady_ reading obtained. Tighten down distributor hold down, reconnect vacuum advance. Check for excessive ping or pre-detonation on a test drive and back off slightly if required. This should be the optimum timing for pump gas, tho may have to adjust springs or mechanical advance in distributor to take advantage of it. Continue to back off in slight increments till there is no ping on acceleration if required.

Look for a scribe or mark on body of distributor from previous owner, this may help too. Make your own for reference. Just a slight turn makes a big timing change, about the width of a pencil line on the body of the distributor is roughly 2 degrees timing.

 

Not homed anything. Timing light is 4 months old.

 

LOL! Yes I know timing light flashes like a strobe Light. Mine only flashes when it gets close to being in time. If it's way out of time it will not flash at all. Thanks for vacuum advice.

 

Ok, you guys are gonna think I'm nuts....BUT!! I've been struggling with these exact symptoms with my 76 f250 390FE...been replacing, hunting, pecking, testing..with beers, 'shine and frustration to follow!! Finally I told myself to start over from the basics, (fuel and fire!)
I checked the ol' squirter(the carb) and I could physically see gas getting in her...

I have an inline spark checker I installed and it was sparking, ALTHOUGH!! the spark looked funny in the checker. On a running 75 F150 390FE had a hard yellow bulb, on the 76 had a dimmer, more blue look...

SO...I got a smile, and another hard drink, and started checking the fire side of things. Turns out the Igntion Coil tower was fried, to a crisp under the boot! I had a spare one in the barn, replaced it and, for F sake, it runs like a top!! No more stall, idle, revs, fixed!!

I thought I would share a smiling moment of revelation. Hope it helps.

 

Good diagnostic technique - the backing up and rethinking part. Also important is an incubation period. That is, go do something else and let the subconscious processes sort things out. A nip here and there maybe helpful for some. YMMV.

 

Yes I had to take a breather. I am going to run a compression test and see what I come up with. Have any of you ever heard of fuel line vapor locking? It's been storming here all week so can't check anything. The truck actually is acting like my lawn mower did 2 years ago. The fuel line would vapor lock for 30 minutes and then run like a dream, for 30 minutes and die again.

 

Glad your diagnosis worked out for you. Can't wait till my story has a happy ending.

 

The latest. I did a dry compression test and these are the numbers. 110 to 120. All plugs black with soot. I cleaned the plugs and reinstalled. Brand new carburetor, I can turn the fuel mixture screws in all the way, and nothing changes. Timing is set.