Timing advice

If you have made mods like a cam carb and exhaust the factroy timing in the distributor is not going to me ideal for the engine any more. The total mechanical advance numbers people have sited are good ball park numbers but it will take getting the car on a dyno or many runs down the drag strip to zero in on the best setting. The same for the rate at which the mecahnical advance comes in. The ball park for that is some where in the low to mid 2000 range. Most stock distributors have it well past 3000 and some of the early 70's emission distributors it won't all be in to 4000 or more. Vacuum advance can be tweaked by driving the car but total advance with vacuum should be in the low 50 degree range.

If you are really interested in dialing in your distributor here is how I would approach it.

1. Don't worry about initial or total timing for this step. With your vacuum advance disconnected. Using your timing light and a tach increase the rpm until the timing stops advancing. If it's in the 2000-2500 range you are good to go. If it's over 3000 rpm you need to change the springs in the distributor. There are usually one heavy spring and one lighter spring on the counter weights under the points/pickup. If you replace the heavy spring with one of the light springs from the Mopar Performance spring kit that should get you back into the 2k to 2.5K range. Using both light springs and the advance will be all in just above idle which will likely cause detonation problems. Optimizing this will make power improvements in the mid range.

2. This step you will be finding out what the engine wants for initial timing and you will need a vacuum gauge. Increase the initial timing is small increments (2 degrees or so) until the manifold vacuum stops increasing. Rember to reset the idle speed back to what it was when you started after each increase in the timing. Once you find the initial timing for max advance check to make sure the engine starts OK. You could have a situation where it wants the timing to be far enough advanced that ignition will fight the cranking of the engine. If you have this situation you will need to back off a couple of degrees at a time to find the point the engine starts well. You will likely find that the engine is happeist with initial timing of 10-15 degrees. Optimizing this setting will improve the throttle reponse off idle dramtically.

3. Now using your set back timing light rev the engine until the timing stops advancing, now see where the total timing is. If it's in the 32 to 36 range your are golden but it's likely a lot more if the distributor is from a low performance or early mid 70's engine. If it is then you will need to rework the slots in the advance mechanism or look for a distributor with less timing in the slots. The top half of the shaft with the slotted piece that the weights act on should be stamped with the number of distributor degrees of advance, double this number for crank degrees. If you aren't inclined to get this much into the distributor tweaking then just set the total timing in the 32-36 range and take the hit on not having optimal initial timing.

4. Now for vacuum advance. The arm on the vacuum pot is stamped with the distributor degrees of advance, again double this number and add it to the total advance number you have. If it's in the low 50's you are good to go. If it's not then you will need to pick one up that has the correct number of degrees.

5. Most all mopar vacuum advance modules can be adjusted by inserting a small allen wrench into the port the vacuum line connects to. The adjustment sets the amount of vacuum at which the pot starts moving and the vacuum level to reach max advance. Adjusting this is a trial and error excersise. You want it to come in ASAP without causing any part throttle detonation. Getting this dialed in will maximize your mileage at steady state cruising and with $3/gal it's well worth the time.