Running rough, low idle, no throttle SBC 327

[Frylok]

I have a 67 chevelle with a 327 in it. I tried setting the timing to 8 BTC and I go to hit the throttle and instant backfire, runs rough and can barely drive it. I checked vacuum and only have 10 lbs. I put my hand over half of the carb and it raised the idle and went up to 15lbs. It has a little exhaust leak. Will the exhaust leak(at head gasket not collector) cause it to backfire that much and have that little vacuum? It should be around 20lbs. Im thinking of replacing the exhaust gaskets, intake gaskets and reset the timing making sure the piston is at TDC. Is there ANYTHING else that could be wrong that I am over looking? I also replaced the spark plugs, some of them wet and black.

Set up is a 327ci
Camshaft is hydraulic flat tappet( dont know anything about it)
compression... dont know
Intake is a off the shelf edelbrock performer
Carb is a edelbrock 650
MSD6a box

[10wideBu]

Sounds like vacuum leak,fix them both. I would set timing around 12-15 base and mid 30's total.need to know vaccum at idle and put a power valve half the value.Is fuel level correct and pressure. You need about .040 on transfer slots,If idle is still off adjust the back the same.idle screws start out about 3/4 from bottom and adjust to highest vacuum reading. You need to get basic tuning down before you start changing pumps,cams,squirters,jets and or air bleeds.Hope this helps.

[10wideBu]

Also forgot power valve is probably blown out. you can test it to see if it is bad. What plugs are you running

[Frylok]

Carb is completely rebuilt. Engine has some cracked valves, Im replacing it with a 355ci 400hp if no body buys it soon from me.