how to adjust vacuum advance

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gotdust57@yahoo

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i want to add some timing to my 73 360 duster with electric choke if it matters, how do i set it with vacuum advance, and what do i need to do it that way or can i just plug off vacuum at dist and do it there? i want about 38*. thanks
 
stick it in the port were the hose goes on,youll feel the right size wrench engage.Its best to make small adjustments,like a quarter of a turn at a time,to get the amount of advance you want.All this has to be done after you get initial,and mechanical advance set were you want first,of course.The vaccum part is for street driveability,more or less.
 
so do i really need to set vacuum advance inside port, or can i just turn my dist counterclockwise until i get my 38 on light, i have actron digital timing light that i can scroll up down buttons until i get my number, and what is advantage of doing inside of port, trying to learn so i dont mess it up.thanks for your help
 
If you twist the distributor you'll be changing your initial timing. And you may not want to do that. Course, if your initial isn't where you want it.....
 
what i have is 73 duster with 360 and i put in pertronix ignitor ingition and flame thrower coil, i set my plugs at.045 and was told i should adjust my timing to about 34 or 38, i think my timing is only about as high as it would go on timing mark about 10 or 12 i believe, so i was thinking i could adjust light to about 38 and turn dist till i get it on mark, i dont have tape to go by and forget about vacuum advance, does this sound right? thanks
 
With an adjustable timing light yes you set your light to the total you want then zero the mark with the distributor. Remember you only want to consider your vacuum advance as part throttle cruise using ported vacuum. Setting your curve for a street car with vacuum advance is not as easy and the all in at 2000 ideas of old may not work in your environment, elevation and density altitude. I like weak but not flimsy springs that give you a smooth curve to about 3300 and find out just how much initial I can get away with on hot starts before shortening the advance slots under the breaker plate. Your desired cruise RPM plays a big role in how you set this up to achieve maximum mileage without detonation or "ping" and overheating issues. If you are running EGR you can get away with alot more vacuum advance as well...

HTH

Belden
 
With the vacuum connected you should have about 50* at about 3000rpm.

Without vacuum, you should have about 34* total at around 3000rpm by turning your dist in small increments.. Once you get 34*, bring it back to idle and see what you get. You should be between 12* to 18*.

If you can't achieve these kind of numbers, your dist will need to be recurved.

Once you get 34* total you can adjust the vaccum from there with the allen wrench in the vac pod.

you don't want any ping whatsoever.

Your plug gap seems excessive. I would not exceed 38 thou gap.

Jim
 
my first time timing, when i get my 34 or 38 since i do not have tape, do i point at 0 or mark, how will i know when i have my 34 or 38, be patient i can build you a house but new at timing and want to learn? thanks
 
gotdust57@yahoo said:
my first time timing, when i get my 34 or 38 since i do not have tape, do i point at 0 or mark, how will i know when i have my 34 or 38, be patient i can build you a house but new at timing and want to learn? thanks
Click to expand...

Not sure about a 360 balancer, but a 340 only has a slit across it. The slit lined up with 0* on the timing tab would be TDC.

Anyway.....just set your light to 34*, loosen the dist , get a helper to rev engine to 3000rpm, then turn the dist until the slit on the balancer lines up with the 0* on the tab. Make sure the vac line is plugged at the dist so no vac timing is included at this point. At idle, shoot the timing marks. Bring the digital reading down on your timing light until the slit and 0* lines up. What did you get? That would be your initial timing.

Try that for now.
 
NiceFishEh said:
With the vacuum connected you should have about 50* at about 3000rpm.
Click to expand...

Vacuum advance only works when there is high manifold vacuum, rpm has nothing to do with it. The only time you will see 50 degrees is when you are cruising with the rpm above the point that full mechanical is in, the throttle is mostly closed and there is high manifold vacuum.

gotdust57, if your 360 is mostly stock you should not need to do much to your distributor. The distributor will have around 24 degrees of mechanical advance built into it. So you initial timing at idle (vacuum advance disconnected) of 10-12 degrees BTDC will give you the 34-36 degrees of mechanical timing the motor will want to see. If you have a dial back timing light you can confirm this by setting the intial then reving the engine until the timing stops advancing and use the dial on the light to bring the mark on the damper back to the zero mark on the timing marks.

You will likely find that it takes well in excess of 3000 rpm to get the timing all in. This is where you can make a noticable difference by changing the springs and having it all come in in the 2000-2500 rpm range. If you pick up the Mopar Performance spring kit that has two springs in it replace the heavier of the two stock springs with one from the kit. Note: using both will have it all in at to low and rpm for a street driven vehicle.

The arm on the vacuum advance module will have a number stamped on it, something like 7, 8, 8.5, etc., double this number to get the number of degrees of advance the vacuum advance can add. Add this number to the total mechanical advance to get the 50ish number previously mentioned. Remember the vacuum advance has no impact on performance, its there to improve cruising efficiency and mileage. The engine will very seldom see all 50 degrees of timing.

To adjust the vacuum advance without a ton of trial an error you will need a vacuum gauge and a vacuum pump with a gauge. Hook up the vacuum gauge to a manifold source and drive the car with the gauge mounted so you can see it. Find whet the manifold vacuum is when cruising at a steady state speed on level ground. Now use the vacuum pump to see what vacuum is required to get full stroke of the vacuum pot. Now you use the allen wrench to adjust the pot so the full stroke is obtained at your steady state cruisng vacuum. Now drive the car if you have no part throttle detonation your ar done. If you do you will need to back off on the vacuum pot adjustment until you don't.
 
Thanks Dave, Im a fair wrench but this was somewhat of a mystery to me. Good explanation. Could you hook uo a vaccomn pump to the canister while running to duplicate manifold vaccumn?
 
Yes you could but it seems to me that it would be easier to measure your cruising vacuum then use the pump to adjust the vacuum advance to match the engine vacuum.
 
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