You did get another #30 pilot jet so they are both the same, right?
I agree it could be an air leak.
The rubber carb boots can be a likely culprit.
If you have replaced them with some new, aftermarket boots, it is easy to over tighten the bolts and distort the rubber boot.
I usually use the same sealant that I use for the crankcase halves and spread some on the surface where the boots attach to the engine, then snug down the bolts without distorting the rubber.
Are the rubber gaskets in the top cap of each carb still in place and good condition?
Yep, the impulse line needs to be absolutely perfectly air tight from end to end.
Some people use ether, but I prefer to use Gumout Carb Cleaner (maybe a little safer) and spray around likely trouble spots for a potential air leak.
If you find one, the Gumout will let you know in a hurry.