Testing Your Distributor
How to ensure your distributor is giving your engine what it needs, when it needs it.
You must keep in mind that the specs listed in the Old Volks Home website are for a "new" distributor, which yours is certainly worn-in at least a little unless it's brand new. It's probably not bad; just worn-in.
To test it, just follow these simple steps:
1. Warm your engine to it's normal operating temperature.
2. With a timing strobe, note where your timing is set at and write it down.
3. Increase the RPM at the carb and bring it to the top of the first RPM range in the timing curve. Note how much advance you get and write it down.
4. Repeat step #3 for the other RPM range(s) specified for your distributor. Also note the TOTAL advance or the point at which the spark advancing ends (both RPM and # of degrees)
NOTE: You should do these steps both with the vacuum canister connected an well as with the canister disconnected and plugged. This way you can see separately how much vacuum advance/retard you have (if equipped) within your distributor from the mechanical advance/retard (if equipped). This will also let you know if the vacuum canister is working or not.
Compare those actual "real-world" readings with the new distributor specs to see whether your distributor is within specs.
If your timing continually fluctuates a few degrees, there's a problem. Pull the distributor out and ensure the spring between the distributor drive gear and the distributor shaft is in place and that it is pushing up in the distributor. If this spring is missing or has poor tension, your distributor drive gear will move up and down in the bore, causing your timing to fluctuate erratically. Fix this before doing anything else.
If your distributor is advancing too early or too late and has centrifugal advance mechanisms within it, you can change out the springs which are attached to the advance weights to tailor the advancing of the timing to return your distributor to stock specs.
Weaker spring rates = quicker full advance; earlier within the RPM range.
Stronger spring rates = slower advance that will reach full advance at a higher RPM.
You can also tailor the vacuum advance side of the distributor by changing out the vacuum canister you have with one that has the advance/retard rates you are looking for. Just go back to the Old Volks Home website and use their database to find a vacuum advance canister with a more appropriate advance curve.
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Revised: August 29, 2003 .