I recently bought a 57 D100 with a 318 in it. I get it home and start having issues with it back firing through the carb, not running smooth under a load like driving up a hill and the HEI distributor failed. I switched back to a points set up, changed the timing chain, new plugs, cap and rotor. It runs better and the backfiring has stopped but i still can't get it t idle at a lower prm or go in gear without stalling. We had a timing light on it when we finally got it running again at it was 30 before top dead center at about 1700 rpm. Adjusting the idle lower and it will idle rough and stall or stall as soon as it is put in gear. Also, the idle will raise and lower a little on its own so we think there is a vacuum issue but we have checked all carb seals and around the intake with carb cleaner and couldn't find a leak. The only other thing we can think of is that there might be a valve issue that is causing the problem. Any advice you guys have would be appreciated.

do you have good gas ?
check the fuel lines at the rubber connections for cracks. you may be sucking air.
better yet, just replace them. they may be collapsing internally.
have you had the carb apart ? it may be full of gunk, causing the issues you describe.

Have you got he vacuum advance hooked to full or ported vacuum? You have the timing advanced too far at idle. Should be about 18* with the advance hose unplugged and vacuum hose plugged.

you are right stumpy.
possibly the advance weights are stuck in the distributor ?

The fuel lines are in good condition and it has fresh gas and a stabilizer in it. I know the timing is to far advance for the idle but I can't get it to idle at low rpm without stalling but I will get it around 18 and see what that does. I did have the vacuum hooded up and it seemed to make it idle rougher than without it. I can turn the timing back to 18 and see what that does for it.

that's what I was thinking & first tho I would get the timing straightened then I'd close the choke part way & see if it starts to straighten out (vac leak). Keep us posted, this is an interesting one

It's interesting for sure and I feel like i'm going down a rabbit hole each time. I haven't had the carb apart but it looks fairly new. I pulled the manual on it, set the electric choke, checked the air fuel mixture, and the floats. I can make a very small adjustment on the idle set screw and the engine adjust right away. I have a set of points I can replace if I need to but I don't know if that would help. The next thing I will do is set the timing, if I can keep it running, to 18 and let you guys know what comes from that. Thanks for all the help, the spot on my head I'm scratching is getting a little sore so it's nice to have the extra help. Jeremy

Mechanical valve timing retarded? Timing set off a tooth perhaps?