Carb Backfires on '74 Shovel

When kickstarting my '74 shovel, no electric starter, not only is it hard to start but it occasionally backfires through the carb. I have replaced points, condenser and plugs. Set point gap to 0.018 with timing mark visible in window. Also, running an S&S carburator. When running and gas is let off it shoots flames out the exhaust, running straight pipes, no baffles. The carb filter has caught on fire once already. Is the timing off or is the carb needing adjustment? What exactly is the proper method to set the point gap and timing? Any help is greatly appreciated. I'm no fireman that's for sure, and obviously a wanna be mechanic....lol.

So, you wanna advance eh?

You did not mention whether or not you checked out and serviced the advancve unit or not. Your timing might be jumping all over the place if the springs are sacked out or the weights damaged etc. You might have a leaking intake valve or a bad intake leak or several other things. Have you done a compression check?
As for setting timeing / points etc, check this article out.
https://www.directparts.com/static/articles/shovelheadtiming.html

Have not done a compression test yet. Put a dwell meter on the bike and the points appear to be stable. Have thought about pulling the adavance unit to check the operation of the fly-weights. Currently have the carb off and getting a rebuild kit for it. It appears there is a bunch of junk in the unit from having set around for a while.

Well I am now replacing the fly-weight assemble. It definitely had a problem. Not only were the springs not workign so good. There was a lot of wobble in the weights. I am sure this in no way helped the motor timing. After tonight hopefully I will be able to have the bike timed and be in the wind tomorrow.

CD, you were correct. The flyweights were wore out. The springs did not work so good and there was a lot of side - side wobble in the weights. Also checked the manifold seals and found a leak at the front intake. All is good now. Thanks so much for the y'all.