Blueprint 408 carburetor
Making blanket statements about whether or not a metering rod style carburetor will bounce the rods at idle isn't accurate. Not every engine will do it. I've seen some that did it at around 240@ .050 and some that didn't with more.
Not knowing specifics like altitude weather conditions and such and you don't have a complete picture. I know how to tune a Carter style carburetor and have seen instances where there was no solution except to go to a metering block/Holley style carburetor.
Calling someone stupid who runs a multi million dollar business cranking out crate engines every day probably ain't the best response. Johnny is a well respected member here and also an avid drag racer whose car runs consistent 10s, so I'd say he knows a little about tuning. Stupid? I doubt it.
Blueprint needs to use carburetors that give the end user the easiest path to a good running engine. Not everyone who makes crate engine purchases can tune a carburetor to the Nth degree. In fact, that's WHY a lot of people go with a crate engine. They might not have the time and or experience to chase the tuning issues a metering rod style carburetor can sometimes give with camshafts that have a lot of .050" duration and tight lobe centers. .....and that is a FACT that some engines simply exhibit that phenomena at idle speeds. I've run out of spring and rod combinations chasing it before, swapped to a Holley style carburetor and bam it was gone on the first hit of the key. Sometimes, there's absolutely nothing you can do to stop it. I guess maybe if you live in a perfect bubble world like Bewy and AJ, everything you touch is perfect.