A couple of years ago I was building a Pontiac powered 4x4 1953 Ford truck. I had spent a ton and a half of money on that HO 421 and finally the day came to fire her off. She spit and puked a couple of times backfired through the carb but no go. I went back to my Motor Manual for the Pontiac. I had ther cylinder numbering sequence right, I had the firing order right 18436572 same as most Gm's. I pulled and checked the distributer and everything was good to go. Still spit, puke, backfire, I go back to the book and pull the dizzy redo everything 18436572 sequence is correct turn the key-- spit, puke, backfire. Man what could be wrong????? Back to the book FIRING ORDER Pontiac 421 HO 18436572-- Check, Cylinder # Sequence Check. Turn motor over #1 cylinder in correct location, turn the key SPIT, PUKE. BACKFIRE....
Pull the intake, pull the timing cover, reset the valves, check timing marks for timing chain, Everything and I mean everything is as its supposed to be. I redo everything for the 6th time, before I turn the key I go and recheck the BOOK.. Firing Order 18436572, Cylinder # sequence, Man what is this in the third column?? Engine rotation Pontiac all V8's "CCW", Can it be that simple? Or maybe the question should be --Can I be that stupid?

Rewire the dizzy--- 18436572 this time CCW-- Turn the key, Varoooom I had me a gen-u-wine fire breathing monster on my hands. I felt real silly for doing that 6 times before I finally got out of my own way.

Morale to that story is check everything and ASSUME nothing..

Roland