I set my timing where TDC is right on with the timing mark. Then I’ll drive it a few miles then check it and it’s off by an inch or more. What is going on?

 

Your damper may be sliding. Scratch a mark across the front of it and unto center hub. Drive and check. Your distributor and engine have a chisel mark that was done at Ford when engine was initially timed and then stamped.

 

If your engine is still running the same then it might be the outer ring on the harmonic damper is slipping. The rubber between inner and out rings has deteriorated and you need to replace the damper.

If there are other symptoms such as stalling, rough running, misfires, etc, let us know.

 

Could also be the roll pin about to shear on the distributor drive gear. Been there, done that.

 

or the timing chain is super loose yet i agree on the damper slipping first

 

Not sure how to do that/understand…

 

The idle goes way up. It seems to be getting worse. I can barely drive it now. Sometimes it will be hard to start. Idles fine when I first set the timing but changes quickly as I’m driving. Idle changes and I have to keep reving the gas to get idle to drop at a stop sign. Sometimes it will other times it won’t.

 

hmmm, idle changing means the ignition and/or cam timing is changing so it is probably not the damper.

The distributor gear/cam gear could be worn and the distributor is skipping teeth
The roll pin holding the gear on the distributor shaft could have sheared or is about to
The timing chain is loose and skipping teeth or the nylon timing gear is broken and skipping

You can mark the the base of the distributor and the engine block, then pop the cap off the distributor and mark the body of the distributor where the rotor is pointed. Remove the hold down clamp from base of distributor and pull it out, inspect the gear, and roll pin, try and look into the hole and check the cam gear.

If all that looks good, you'll have to dive deeper into it and get the timing cover removed to inspect the timing chain.

 

Got it. Does this tell you anything?: When I loosen the distributor hold down bolt and rotate the distr., the rpm’s change fairly dramatically. Or is that normal?

 

Yes, you're adjusting your ignition timing, that will affect idle speed, as you advance (clockwise rotation) idle will increase, when you retard idle should drop. You want as much ignition advance as the engine will handle without detonation. You can try to set timing by ear, but timing light is preferred. With vacuum line disconnected from distributor and plugged, your initial timing setting should be in the 8-12* range for a stock engine. You might need to toggle back and forth between adjusting timing and idle speed, you want to keep idle 700-800 rpm (for automatic trans this will be when in drive, for manuals when in neutral), if you let idle get too high, mechanical advance will start to kick in and will affect your timing readings.

Once initial timing is set you can reconnect vacuum line, typically to what is called ported or timed vacuum which will be a small port that is higher in the carb body than the throttle plates. After timing is dialed in, its a good idea to adjust idle mixture of your carb too, for that I prefer a vacuum gauge, but that's another rabbit hole to dive down, once you determine what is causing your timing to fluctuate and get that fixed first.

-EDIT- make sure your choke is fully open and the fast idle cam for the choke is not bumping up the idle speed when you are making these adjustments

 

For a quick check unhook your vacuum advance and see what happens.

If you're hooked to manifold vacuum on your advance it can cause issues. if it's not that your mechanical advance probably has broken springs or some sort of problem.

 

how does this look?

 

Is this the vacuum port you’re referencing? This is coming from vacuum advance (?) from distributor.

 

The gear looks okay.

Grab the gear and twist it back and forth, if it rotates on the shaft at all the roll pin might be sheared, or is bent and about to shear. If it's solid, that's not your culprit.

Next, holding the gear, grab the rotor (if it's removed, put it back in) while holding the gear twist the rotor clockwise and counter clockwise, it should move a little with the shaft and gear held firm, what you're doing is moving the mechanical advance, when you have moved the rotor let go of it and it should snap back into place, that will confirm if the advance springs are still intact. If it doesn't snap back or the rotor moves easily without any resistance from spring tension, your mechanical advance springs are broken. If the rotor doesn't move at all, your mechanical advance is froze in place probably due to rust.

Since you got it out, if you have a hand vacuum pump you can test the vac advance, hook up your pump and pull 10" or so of vacuum, you should see the arm going through body of dizzy connecting under the rotor move, if it doesn't move vacuum diagram is shot, of it does move, keep the vacuum on it for a minute or so and make sure it holds vacuum, if vacuum on the gauge drops, your diaphram is leaking.

If all those things check out good, I'm thinking you have an issue with your timing chain.

 

Yes, that should be it, it is higher than throttle plates, as soon as you start to open the throttle plates, there is a hole or slot in the venturi that will start to get vac signal due to air flow and will pass that vac signal to the advance on the distributor. The vac advance provides ignition advance under no or low load conditions so the engine runs more efficiently in those conditions. Under load or wide open throttle that vac signal goes away and the vac advance is taken out of the equation, that's where mechanical advance comes into play due to increase in RPM.