henery riffle help my timming

i know everyone heared this before but im stumpped. my big block has a healthy cam and low vac. for timming i plugged of the advance and set inital at 18 deg. at 16, 14, 12 it idles rogh. i have a petronix hei with black springs in it i get 24 deg more at 6,000. the car backfires when i rev it in park and wot after i let my foot off. i got the right springs in the edelbrock carb and i just need some advice im not going to run the vac advance canister at all forget the gas i just want the best timming set up

the motor has 10-5 static compression, no air leaks plugs and wires are good. ive got the idle set at 1,000rpm

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.

its adj and the canister is set at 10. i under stand about the inital being to high but at 10 or 12 degres the engine ha horible idle and very low vac.

I realize you said you weren't going to run the vacuum advance, but are you shooting the timing with the vac advance connected?
It's supposed to be disconnected while you set the initial timing.

Barring that, set the initial with the engine stopped.

I encourage you to run vacuum advance.
Without, you'll more than likely overheat in summer traffic and during long periods of idling.

Do a search for an article posted a while back.
Titled, "Got Time?"
It may help you understand where you're at and where you're going.

no i have the sdvance pluged off and im timming it without it pluged in