SMB 350 Timing and fuel consumption problems??

I have a SMB 350 in my Jeep CJ7 which I rebuilt recently. The problem I am having is with vac advance disconncted the lowest I can set timing at with a light is about 30 degrees BTDC. Anything less and i backfire through the carb and cant get her to go over 40 MPH. Reset at 30 + and she runs great, with the acception of fuel mileage of about 10 MPG. THis does have a brand new Edlebrock 600 on it, originally thought I was having some problems with the old Carter that was on it before. I have restabbed the distributor several times and with the same outcome. My question is, Could i have gotten the timing chain off by a tooth or two to cause this problem. I would like a little advice before I go ripping this back apart. The jeep sits on 36's and does take some considerable work to get down into the engine compartment for this kind of work. Any help would be greatly appreciated. Thanks, Ryan

did the out side ring slip on the damper i have see this happen this i check when asem the engine on no1 checking with dial indicator for tdc then you can check the timing marks .is the tab rigth for it ??

I have used a couple of harmonics, thought that could be the problem, also got new tabs for each harmonic, and all end up with the same result. Thanks, Ryan

As was suggested to me a while back,,if you suspect your dist to be out by one tooth,,then try moving your plug wires over by one position,,clock wise or anti clockwise,,till it runs right with proper advance.

do you have a vacuum gauge?? see wath you have and do have the vacuum pull on ported on the carb:whacked: