Do you have a cap on the 3/8” bung in the center front of the 2GC?
Sure sounds like a vacuum leak with the surge.
Did you follow the IAC initial setup in the manual?
Nice job. I’ve installed 5 2GC large bore but all of them have been on FJ40s.
Mosley Motors sells the adapters that I used. Yours looks sweet. Nice work.
My latest.