Big Block MPG

Jesus Chrysler said

I took the car for my longest cruise since I’ve had it this past weekend. 70 something miles partially around town a little bit of twisty back country roads Some decent open highway miles in about 30 minutes of crappy traffic. Mileage drop to about 8.5. Has me wondering if gas is evaporating while the car sits for a week and doesn’t move.

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More likely it's evaporating while sitting in that crappy traffic. Might want to look into a vapor return system and an insulating carb spacer if you don't already have one. Also how is the carb jetting? You might be able to lean out the low-load/cruise circuit without any bad effects. I picked up 3 MPG on my old 360 after installing an O2 sensor and finding out I was crusing at 13.5-14:1 AFR so I leaned it out to about 15.5:1. I also noticed after leaning it out the oil took a lot longer to turn black and no longer had any gasoline smell to it. And the exhaust wasn't so smelly.