Timing Marks on the 273 [66 Barracuda]

Much of this is a cut and paste from past posts but covers the info you asked for.

The timing information is in the operators manual and the service manual.
You can look at mymopar.com for digital service manual.

Everything below assumes a factory distributor on a factory engine. Replacement distributors may or may not have the factory timing curve.

Initial timing is set with the engine at low rpm and the vacuum advance disabled. Always!
The rpm is important. If the rpm is too high, then the distributor will already be advancing.
-------------------------------------------------------------
Needed is a timing light and a tachometer.
A 'distributor wrench' is handy but not neccessary - the hold down cap screw can be gotten to with sockets and extension or a box wrench with some creativity.

The initial timing of a '67 273 Plymouth is 10° BTDC at 600 rpm. Plus minus 2° is still within spec.

1. Clean the timing marks.
2. Connect the timing light's inductive pickup. - Place it over the #1 spark plug wire (front driver side) so the wire goes through the opening. -Route the wire so its clear of exhaust and the fan, belts, etc, and so you can hold the light pointing at the timing marks.
3. Connect the tach/dwell meter if that's what you have for a tach.

Start the engine.

1. If its not warmed up, get the engine warmed up.
   
2. Kick it off fast idle. When it will run at slow idle (no choke), connect the timing light power. Most timing lights get power from the battery. Positve clamp to positive, the other one to negative.
   
3. Remove the hose from the distributor's vacuum advance. Stick a golf tee in the hose. Alternatively, remove the distributor vacuum hose from the nipple on the carburator's side. Place a rubber cap over the nipple.
4. Read the RPM and the Timing. Write them down
   
5. Adjust the idle speed screw to change rpm and read the timing again. (write down how many 1/8 or 1/4 turns of the screw you make so you can go back if needed).

You should be able to measure and set the timing at 600 rpm.
If you can do that. Great!
If you want to check the mechanical advance is working, turn the idle speed screw in to bring the rpms up. Write down the new rpms and the new timing reading. Do this up to the top rpm of the tach/dwell - usually this is around 1200 rpm. If you have an dash tach and you want to measure at higher rpms, thats fine. When done measuring, return the idle speed screw to 600 rpm.

Reattach the distributor's vacuum hose to the vacuum port on the side of the carb.
------------------------------------------------