1987 Honda CRX ignition timing and mpg?

hey, i have been trying to set the ignition timing on this carborated 87 crx. I have two conflicting views on how to do this, weather or not to disconect the vacuum advance. when i do dissconect it and set the timing at idle, as soon as i re connect it it advances the timing, is it suposed to do this at idle? or do i need to set the ignition timing with the vacuum advance hooked up? Also the car should be getting great gas milage, but i am bearly getting 160mi to the tank? i am wondering if this is related to the timing, or maybe a worn carb, it has all new fuel filters, air filter, fuel lines and fuel pump.