Stock SBC 350 Crate Motor valve chatter under load
Try F to see if it makes any difference. G is all in by 2500 rpms. F is 3000 rpms. After adjusting settings rev the engine to 3000 rpms and check total timing for 32*. GM recommends 34* on 87 octane. But you might have to wait until you solve this problem. If you can check the oil on the dipstick see if it smells like gas. If it does change it. Get a vacuum gauge and tune the carburetor and do some of the other checks in the instruction book. When you are able to get it right and want to hook up vacuum advance try F3 #1 knob 4, #2 knob 6.