Does the dipstick smell like it's got fuel in your oil?
Do all the basics with a Holley. Float level would be the first item to check. Maybe lower it an 1/8 turn from where it is if it's set OK now.
If that has a decent tune up on it, there's no reason it shouldn't be getting in the teens for mileage around town.
Is the speedo correct?
The fuel is going somewhere?