Carb Tuning / Vacuum Problems?

Firing order, double/triple check it.

Plug off ALL the vacuum ports at the carb. Eliminates any secondary leaks

Check float level and baseline the idle mix screws at 1.5 turns out.

Set the timing at about 16-18* initial.

If it idles above 1000 rpm, it may be bleeding mechanical timing in and that gets pulled out when you drop it in gear. You time it for 12* at you 1300 rpm and it drops to 7-8 when in gear at 800 rpm. Your engine should idle EASILY at 850 rpm, imho.