Decide which slot you want to use and if necessary remove the upper advance shaft retaining clip and springs so you can lift and rotate the shaft in to the proper position. If ordering a distributor from a parts store ask for one for a 1975 elite with a 460 4v engine. You will be more likely to get the lower number advance slot like a 10L or 13L rather than the 18 or 21L's. If you have a distributor with the larger numbered slots limit rotation via welding the slot smaller or placing a bushing around the pin to limit total shaft rotation.
To figure approximate slot width for a given advance figure Multiply the number of desired centrifugal degrees by .013" then add .150" to account for the width of the stop pin.
8L slot = 16 degrees centrifugal advance = .358”
9L slot = 18 degrees centrifugal advance = .384”
10L slot = 20 degrees centrifugal advance = .410”
11L slot = 22 degrees centrifugal advance = .436”
12L slot = 24 degrees centrifugal advance = .462”
13L slot = 26 degrees centrifugal advance = .488”
14L slot = 28 degrees centrifugal advance = .514”
Step 6
install the springs from the recurve kit and bend the tabs to keep tension on both springs so the advance shaft returns to its idle position
Step 7
Reassemble in the reverse order. Breaker plate, Reluctor, Vac advance dashpot and return the little clips to their proper place.
Place the reluctor back on the shaft in its original position and align the roll pin slot in the reluctor with the roll pin slot on the upper distributor shaft. Carefully place the roll pin into place after fully seating reluctor on shaft and gently push it back into place with a hammer and a small punch. The 1/2 slots in both the reluctor and in the shaft together make a round hole for the roll pin.
So what about Vacuum Advance?
Vacuum Advance
Under conditions of light or closed throttle, the volumetric efficiency of an engine is quite poor, and cylinder filling is affected to the extent that the effective compression ratio is much lower than the static or calculated compression ratio. In these circumstances the mixture will burn much more slowly than with a fully filled cylinder and the flame front will reach the piston quite late. This can dramatically cut the overall efficiency of the engine and its economy. Under these conditions the engine will tolerate and indeed benefit from advancing the timing by up to 15 degrees over its normal setting.
The device that usually performs this trick is called the vacuum advance device. The way this works is to exploit the partial vacuum that is present in the inlet manifold when the throttle is closed or partly closed. A tube is connected from the manifold to a sealed diaphragm in the distributor, which in turn is connected to the distributors base plate. The suction deflects the diaphragm which turns the base plate against the direction of rotation of the distributor thereby advancing the timing, this gives much better throttle response on part throttle, and far better economy.
Many people who tune engines disconnect the vacuum advance mechanism, and indeed on some distributors it is very hit and miss in operation and can cause anomalies in the timing. All in all however for a road engine, the vacuum advance retard should be retained if it is possible to do so (not always easy with sidedraught carbs). This will have a dramatic affect on economy and driveability especially on small throttle openings and when 'off-cam'.
Most Ford distributors include a vacuum advance mechanism. This consists of a diaphragm vacuum canister, an arm from the canister to the breaker plate, and a hose connected to an engine vacuum source. The purpose of this mechanism is to provide spark advance when the engine is not spinning fast enough to create the centrifugal advance talked about earlier. In other words this is an engine-load dependent advance. This would be a typical situation when climbing a steep hill, or driving at low rpms, light throttle, conditions. In these conditions there is high engine vacuum, so the vacuum signal applied to the diaphragm in the canister, via the hose, will cause a 'pull' effect on the arm, which moves the breaker plate and results in a timing advance. During full throttle conditions there is very little engine vacuum, and thus the vacuum advance does not contribute to total advance.
Vacuum advance is tricky to tune because there is no direct measurement like total. In fact, the reason you must measure initial and total timing with the vacuum hose disconnected is because when the engine is in neutral there no load, thus the vacuum is high, and if the hose were connected you'd see as high as 60 degrees advance and think something is really wrong! The only way to tune vacuum advance is on the road, by feel, and AFTER the initial and total are adjusted.
In short, vacuum advance was developed to optimize fuel economy and reduce emissions. It is not a bad thing to have on a car which sees a lot of street driving, and in such conditions the engine will perform better with it properly adjusted. However many factory and aftermarket performance distributors do not even come with a vacuum advance. The reason is simply because race cars do not spend much time at part throttle.
Setting Vacuum Advance:
Vacuum advance canisters are usually adjustable with a 3/32-in. allen wrench, as shown here. The small screw inside the housing adjusts the tension on the diaphragm spring. If you detect knocking and loss of power, back the screw out (counterclockwise) to decrease advance. If the engine pops and surges, tighten up the screw to increase advance.
Note:When checking initial and total advance, always disconnect the vacuum advance hose. Otherwise you will get very high timing readings.
Tuning Vacuum Advance
The last step, after the total advance curve is set, is to dial in the vacuum advance if you have one. There should be a vacuum line connected from the carb, or the manifold, to the vacuum canister. There are two types of vacuum sources that you should be aware of. One type is known as "full" vacuum or "manifold" vacuum. This is a direct connection to the manifold, and if the hose is connected to this port you will get vacuum in the line at idle. The other port is a "timed" port, which only yields a vacuum above a certain rpm. At idle the line will have no vacuum. Most carburetors have both ports. On Holley's the timed is above the throttle blades, and the "full" is below, near the base. On Carter/Edelbrock carbs, the timed port is on the passenger side and the full is on the driver's side. The easiest way to confirm what port you have is to hook up a vacuum a gauge and check for vacuum at idle. The preferred vacuum source is the timed source. This way there is no effect on the initial timing setting.
Remember vacuum advance is load dependent, so you cannot check it with a timing light with the car in neutral. The best way to set vacuum advance is by feel, under real driving conditions. Connect the vacuum line and drive the car up a steep, long grade, with the car in high gear and at a low speed, 30-40mph. Occasionally push the accelerator to the floor, and listen and feel for knocking and/or loss of power. If you detect this, immediately back of. This means the canister is advancing too much and you should adjust the canister so the diaphragm is 'tighter', by turning the screw counterclockwise.
You can also adjust the vacuum canister clockwise until it does start to ping and then back it off 2 turns. This should set your Vacuum Advance perfectly.
Read this! Might be some help
1 
Offline
Thread Starter
MS wrote:
. Never found it 
I tried a home-made one butt that didn't fit tight enough. Soooooo like a good shade tree mechanic...........I left it out!! 
