Setting initial advance, at 800 rpm, the mark is a little off the scale. I have a Craftsman dial back light. I moved the dial and at 15 deg dial movement the timing marks lined up at zero. Does this mean there is is 15 deg initial advance? Also, at 2500 RPM the I had to move the dial to 40 deg for the timing marks to align at zero. Does this mean I have 40 deg total timing (not including vacume advance. Vac adv was disconnected for all tests). Thanks

You are correct. I would check the total timing with the rpm higher up. You may have some stiff springs in the old dizzy. Do you have a small block or a big block, because your total timing seems a little high?

It'a a 383. Has stock eddy heads, Holley SA 670, MP duel plane and resto purple cam. Been having a "rich at idle" problem for a while. From what I've been reading here about 38-40 total seems to be the norm.

38 total seems to work good on many BB. But you can not successfully set total advance at say 38 degrees at 2500 RPM's unless you have your distributor calibrated so that it is fully advanced at that RPM. If you were to set it at 38 degrees at that RPM with a stock distributor you would have considerably more advance left in the distributor and it will still be advance way past the designated RPM.

The mechanical advance weights must be change. There are spring kits available to do this. In order to check where your advance will take you you can hook up your timing light and watch the timing mark advance as then engine speed increases but with a stock distributor the RPM's will be quite high before the mechanical advance is fully advanced.

I'd rev it until it wont advance anymore(vac adv disconnected) & lock it down at 38. You would need a tach hooked up to know the rpm at that point where it wont adv any higher. Is this a stock dist w stock springs? 38 total will get you pretty close to ideal & if there's no pinging as you run it up thru the gears you're Ok though if it still has the original springs, the light one & the heavy one with the elongated loop on one end you would very likely gain by changing it(still keeping the total at 38). Also note what your initial is at idle before/after(any)changes.

It's a MP electronic dist with orange box. It's been in the car for five or six years. I have no idea what kind of springs are in it; whatever MP put in it from the factory. Never had a problem with pinging, even here in AZ. Only about 9:1 compression.

I believe those have reasonably light advance springs. Your advance may be all in at a relatively low rpm like you initially posted, but you still need to verify that.

The issue with those dizzy's is that they provide too much mechanical advance, which forces you to use less initial timing, which reduces your performance at lower rpm. They solution is to reduce the amount of mechanical advance by limiting the travel of the advance mechanisim itself. This allows you to have more initial timing, less mechanical advance and end up around 38 degrees total.

Once you have that squared away. They work nicely. You may want to find and keep a spare control module stashed in a ziplock bag in your trunk though.

If you're still not happy, you might also want to pull the heads, have them ported and decked to increase the compression, install a bigger cam, a bigger carb and a looser torque converter...

Also, DO NOT TRUST these delay timing lights too far. Sometimes something like a reluctor which is just slightly misadjusted can cause a multi-fire condition in an ECU, or the light itself can be dodgy, and give false readings.

I recommend ONLY that you take the time to scribe the wheel or get an accurate timing tape and CHECK the marks with a dead stop, very easy to do.

MANY of these guys will post "I've never had trouble," or "MY light is accurate" but the fact is, you may not know for sure whether it is or not--all the time.