How much of a timing "jump" are you seeing? A degree or two in either direction is normal because of the inaccuracies of the "Hall Effect" that triggers the coil collapse (producing the spark). Even the latest engines that have the Hall Effect trigger on the crankshaft will have slight timing variations.

 

Use 36* advance , 16* at idle.

 

Hall effect inaccuracies?

 

Check your fuel pressure. Mine would jump more than 4 degrees. My fuel pressure was too high. It was running about 8lbs causing irratic fuel delivery to the engine and when it heated up it got worse. I installed quickfuel regulator and dialed it down to about 4lbs. Seems to have setteled everything down and the timing mark seems pretty stable.

Hope this helps

The Captain

 

Will do, thanks!

Mike

 

Yes, and that's why all of the latest engines use crankshaft triggers. The trigger (Hall Effect switch) in a Pertronix or HEI that is spinning at half of the crank shaft speed gives small timing fluctuations because of the timing chain/sprocket slop and gear lash between the camshaft gear and the distributor gear. Plus the tiny amount of shaft/bushing clearance in the distributor and end play add more timing inaccuracy.

 

And just what kind on sensor is in a crank trigger?

 

AH !! THEN THE ILLUSION OF PROGRESS ....

Car manufacturers went to a crank trigger when they started going variable timing. In overly simple terms a magnet on the crank triggers a sensor when it passes so the computer can tell the spark plugs when to fire based on where the pistons are.
When variable valve timing was simple the relationship of the crankshaft to the camshaft and distributor changed thus knocking the timing off at reduced valve timing.
The camshaft is still chain driven so/but isn't that important to be timed accurately.. never mind.
By going to the crank trigger the car companies did not have to set up and time an engine. This saved a lot of training & time which = money. It also eliminated the distributor with it's rotor & cap.. less to build and maintain. The cars had computers anyway so why not.

In a car with out a computer, the distributor is tied to the crank by a gear and chain set. Fuel pressure, leaking mufflers, open windows, radio stations, etc will not affect timing. Usual suspects are bad rotor, loose cap, bad bearings in the distributor / bent distributor shaft, worn timing chain. Improperly meshed distributor gear to cam gear, loose gear, loose distributor, weak springs on the advance weights.

I would start by setting the idle at 750 RPM , no vacuum and setting the timing. You should get a steady reading with +/- 1 degree.
Most times I found the varying was due to the engine surging and the weights moving. If the RPM is steady and there is no mechanical issue and the timing is moving then I would suspect the electronic module.
Make sure the harmonic balancer is not slipping.

Only once did I find a weak coil cause a slight timing issue, the car was never driven hard, or highway and thus did not show the usual mis-fire or lack of power. Amazingly it did not have hard starting, but would miss after a few miles of driving.

Hope you find the issue...

 

I recently had the same problem of the timing mark jumping around. I traced the problem to the timing light getting a signal from the cylinder #3 spark plug wire in addition to cylinder #1 wire.

I clamped the timing light onto #1 spark plug wire near the firewall where I could get more space between #1 and #3 wires. That gave the timing light a clean #1 signal, and the timing mark stopped jumping around.

I didn't have any timing issues at all, just a timing light problem. I chalked that one up to operator error.