I run the higher grade fuel only because of the non-ethanol component to it. That is the only octane available in non-ethanol at the local gas station. Yes adjusting the idle mixture screw does change the RPM. Wondering if my float is too high or main jet too large. I will try advancing the timing a few degrees and see what it does then.

52 Chevy 3100

Jesus said to him, "I am the way, the truth, and the life. No one comes to the Father except through Me." -John 14:6