there is a gauge, look in speedway or jegs, i think is called a carbsync.. the milage will be less, you are pouring gas thru two openings instead of one. i got 15.4mpg last week mixed driving. i have dual carbs dual exhaust and a 5 speed s-10 trans and 15 inch tires. i have gotten as high as 19.2 averaged over two fillups but i think one carb was not working. mho. ron
