Working on 350 SB Chevy . Just replace cam , lifters , timing chain & gears, new 202 heads . Motor will not start , back fires. Can anyone give advise??????

 

Distributor is 180° out: sending spark to each cyl at its instance of TDC when the exh valve is closing and the int is opening, instead of the other instance of TDC at the end of the compression stroke and beginning of power

 

If you installed the timing set dot to dot & placed the dist in at #1, you are 180 out.

 

Exactly:

We build motors at the dot-to-dot point because it's easy to see and get lined up right, NOT because it's #1 firing (because it isn't). Sure, it's #1 TDC, but NOT #1 firing. It's #6 firing; it's the instance of #1 TDC that's at the end of the exh stroke and beginning of the int, NOT the firing instance.

The correct orientation of the dots for #1 firing is both at 12:00. Exactly one full crank rotation, and one-half cam rotation (engine cycle), away from dot-to-dot.

 

Distributor is 180* out
Timing chain not lined up right dot to dot.
Plug wires on the wrong places on dist.

My money is on timing off due to dist. placement.