Reply to "Carb backfires"

Mikael,
Thank you for the reply.
I am not familiar with this Forum, and can't see how to reply directly to you, but hopefully you will see this.
Google research seems to tell me the following: most likely causes are either lean mixture,vacuum leak and/or ignition timing.
I think I have several open ports to carb, so I will look to plug them. I think timing is more likely.Will check firing order - I think it's ok.
As far as ignition timing goes; how do I check with timing gun if engine won't run? Do I do static timing with # 1 cyl on compression stroke?
When it briefly runs, it seems to be running smoothly, which suggests to me that timing may be close enough and that problem is leaning out?
Anyway, will check all that you suggest.
Thanks again, and maybe Danish heritage connection will be an assist to solving this.

Bill Nelson