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.
