Thread: henery riffle help my timming

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18 degrees initial may too much for that big block. With 24 in the distributor, you're running 42 total. That's at the high end. 34 - 36 should get you there. That would be either 10 or 12 initial.

If you still get backfiring there, you either have the wrong advance curve in the distributor, or you may have a carb problem. Just disconnecting the vacuum advance doesn't always work, because the distributor is designed with it in mind. To get it exactly right, with only mechanical advance, you need to have a good shop set it up for your engine. Otherwise, you're just guessing.

Your centrifugal advance should be all in by 3000 rpm. You can check that with the vacuum plugged and a timing tape on the crank. Set it at 12 degrees, and make sure you have 36 at 3000. If you don't, you have the wrong springs.

Do you know how much advance is built into the vacuum can? If the distributor is new, the instruction sheet should tell you. An adjustable vacuum can might help you get a better idle. Something with no more than 8-10 degrees under full vacuum.

I ran a full mechanical Mallory Unilite on my big block with no problems, but I took it to a shop and had it curved to match the engine and the cam.