You can also check for air bubbles in the coolant with the motor running. Then additionally block the wheels, have someone with the brakes on load the motor in gear slipping the clutch, and check for bubbles. You will see water pump turbulence, but not bubbles which would indicate head gasket.
A better test is a Coolant Block Test - tests for exhaust gas in the radiator top tank. Can have done at a shop or do yourself
https://www.napaonline.com/en/p/BK_7...RoCZrAQAvD_BwE
Cheaper on eBay/amazon.
At idle the motor/carb runs off the Carb idle Mixture screw and the GAV, above idle the motor depending on conditions (RPMS/load) runs off the other passages/jets. Above 800 RPM GAV should not have much if any effect on motor running.
Replacement Jets are notorious for not flowing correctly - reason why flow tested replacement jets are recommended when replacing jets. Micing and cleaning is not a substitute for making sure the jet passages are sized properly for proper flow.
An additional way to measure coolant temp is to install a temp gauge via the Head coolant outlet neck.
Also check to make sure the throttle and choke plate shafts fit snuggly in their bushings, another cause of lean running requiring more GAV. Also a cause of poor idle.