mileage. the harder i try the worse it gets...

clipped some coils of another set of springs has a little surge so thinking to much. havent driven enuff to fill up yet and now finding out weve had someone stealing gas from the neighborhood. maybe thats whats happening? been busy with my truck project and work and still havent ordered the calibration kit but planning to very soon. also my d100 has a stock early 70s 318. thinkin of upgrading should i go smaller cam and something besides the eddy carbs? its a 3speed man with 355 geared 8.75.