Nothing like flogging a fresh topic.
As chance would have it I rode an SS today with the snorkels removed, and much like the Monster it felt harsh at WOT. Not as bad, but certainly off. The before dyno runs from the two 900SS I fitted FCR to were both done with std airbox lids without snorkels. Much like the Monster, they were too lean (just not as). As below:
Comparing a few air/fuel traces as below you can see the difference in std jetting fuelling. The Euro spec 900SS and Monster use the same 140 main jets, Y-2 needle jets and 5C19 needles. So theoretically they're the same, but it doesn't work out that way. Light blue is 900SS with snorkels, dark blue without, red 900M with, green 900M without. The Monster is leaner in both cases.
From memory the SS with run was from a 900SS traded in at Moto One that I rejetted after these runs one step leaner on pilot, main and needle. When I rode it it was very nice: crisp and smooth. A salesman agreed. Then it got sold and the new owner complained that it "took a long time to warm up". Showing an issue with the Mikuni carbs that only gets worse when you try to make them work better: you need to make them a touch richer than ideal to get them to work acceptably in all conditions.