Timing, By hand? Options

[Boothy]

Greetings all!
I haven't bothered you guys in over a year I think -you're welcome.

Last fall the new engine started smoking and the tail pipes were black. Sluggish. I think I rejetted at some point but can't recall. Naturally I assumed I burned something up or broke a ring etc. so I put it under a cover for the winter. Bought a compression tester but I was so fed up I just said screw it till spring.

Refreshed and ready to look at it again, I looked online thinking I'll start with jetting. I have Weber 40s on a 1.7 punched out to 2.0. I was at 185 mains but another AI search (I know I'll hear about that) said go to 1.15 mains and 2.00 air correction. Seemed to cleanup last night and I'll run it some more today. But now it pops a little on deceleration. Sounds better -cleaner.

Looking the popping might be a too lean condition, air leak near the exhaust flange, etc. BUT, I had a lot of trouble with the timing mark on the fan so I'm not 100% sure I have it where it's supposed to be. Despite multiple efforts (looking at lots of pictures of the fan marks) I'm just not sure. I know it sounds hack but I'm wondering if I can advance the 123 distributor a little at a time manually.

I'll do a compression test tomorrow to be sure but thought I'd throw it out to the gods.

Thanks in advance!