How and how badly will this crack in the tube in the Venturi assembly affect performance?
It’s only one of them that’s cracked.
It looks like someone tried to fix it with solder at one point.
Does someone have a “spare” 1.23 Venturi 
since I’m half way through rebuilding this thing??
I have a 351W 2v so maybe another size Venturi would work, though I’m not sure about mix and matching carb parts.
yeah, that’s bad. You could solder it up and then use a number drill to make sure the holes are opened up properly. (Use an existing clean hole to size the drill.)
I haven’t soldered before but maybe it’s another archaic skill I could learn for this task.
What solder would you recommend for this that I could apply with a simple soldering tool? It already has a solder on it already so perhaps I should use a similar substance.
This is not going to be easy as you have a gap to fill. You will also need a soldering iron that is at least 100 watts. If you send it to me I will do it for you for free. I have the right tools and experience. I also have a couple parts carbs that I will dig out and see what I have there.
I would just buy another one. Whole carburetors are easy to find and cheap.
https://www.ebay.com/itm/154620820547?hash=item24001e7c43:g:07UAAOSw6PRhSnbI
You guys crack me up.
Bill, if you don’t have a Venturi I’ll probably just find one on eBay.
Royce, one of the EBay items says 1.23 on it but is described as 1.08 so I have contacted the seller.
OK so I bought one on ebay that the owner says has tubes that are intact. Carb looks to be missing things but I just need the venturi assembly which hopefully has similar specs. Off an earlier Mercury model. https://www.ebay.com/itm/184397764881