Either I'm losin my mind or just gettin old. I just changed the intake manifold and carbs on my 350 now it won't start, backfires both through carbs and tailpipes (not at the same time). I timed at 8 BTDC (nice cam), firing order 18436572 with 1 being front driver's side of engine. I've cranked the darn thing til the battery's nearly dead now. What the heck am I missing??? Thanks.................

Rotor?
Check wiring, again, both primary and secondary.
Use a timing light to set timing while cranking or set 8*BTDC on the mark and use AM radio to set distributor.
Fill fuel bowls with fuel.
Prime fuel line from tank to pump and pump to carb(s).
Charge battery.

Thanks Everett. I'll defintiely check wiring again. I don't know what you mean by primary and secondary though. Please forgive my ignorance on that one...

Set engine to tDC with #1 piston at the top checking rockers that it is on the fireing stroke
Check rotor is pionting to #1 and NOT #6

I don't know what you mean by primary and secondary though....
Primary side is the low voltage side, ie, 12 volt side.
Secondary side is the high tension, ie, high voltage side, coil, plug wires, dist cap, & rotor, wire separators/holders.

Your welcome.

Either I'm losin my mind or just gettin old. I just changed the intake manifold and carbs on my 350 now it won't start, backfires both through carbs and tailpipes (not at the same time). I timed at 8 BTDC (nice cam), firing order 18436572 with 1 being front driver's side of engine. I've cranked the darn thing til the battery's nearly dead now. What the heck am I missing??? Thanks.................

Check the obvious first. is dist 180* out? Are wires to correct post aligning with rotor?

Distributor position.. 180 out..
wires..

Thanks guys. I think too often we get fixes from you guys and never bother to come back and say thanks. My dizzy was 180 out! Fixed that and my 350 literally roared to life. Just to let you know, I'd put an Edelbrock crossram intake with 2 Holley 450s on it. Medium cam and headers. The combo seems to work really well.......

Thanks again guys......