Divide your old injector size by the new injector size to get the variance. For example: 36 / 42.5 = 0.847. So... your new IFR table shall be 84.7% of the old table (highlight all cells in the IFR table, right-click, select CUSTOM, click on PERCENT, enter 84.7, click ok, this is what i would have to do since i have a DHP.

*taken from the tuning bible*