[Jim Colman]

Maybe I can help a bit. I also had a 351C that was experiencing some backfiring problems. Turned out that it was simply a timing issue.

First, make sure your distributor isn't installed 180 degrees out of whack. The rotor should be pointing to the number one plug terminal when the number one piston is at TDC. You can pretty much gauge TDC by taking your plugs out, and hand cranking the engine. You will feel a whoosh of air come out the spark plug hole and your rocker arms will be in the closed position.

The timing needs to be set with the vacuum advance plugged. Also, make sure your vacuum advance isn't plugged into a timed vacuum port on the carb.

Total timing should be in the 34-36 degree range with initial timing set to about 12 degrees.

Your distributor could also be part of your problem. According to one person who helped me with my problem, most non performance Ford distributers have too much mechanical advance for performance use. The distributers don't achieve full advance until over 4000 rpms and may have as much as 30 degrees of more mechanical advance built into the distributer. This doesn't allow enought initial advance for good response. A distributer with 20 degrees mechanical advance will allow you run around 16 degrees or so of initial advance. For best results, a distributer needs to deliver only around 20 degrees of advance and have all advance in around 3000 rpms.

You can buy ans MSD billet distributer that comes with a variety of springs and bushings to control advcance rate and total advance.

I kept the duraspark distributor on my car and simply reset the timing. It made plenty of power for my street use.

Hope this helps.

Jim