Every two years in December is the dreaded smog check for my 79 T/A with bone stock 403. Bleh.. Long story short, two years ago failed miserably as gross polluter. Hydro carbons sky high and various vacuum lines missing: Took her home and found numerous vacuum leaks, reconnected lines to vapor canister and carb, set timing, and fine tuned carb best I could and barely failed second time. HC a hair above max allowed. Notice NO right at the average: Decided to replace the catalytic converter and HC dropped big time but noticed NO went way up from 455 to 745: Question - Although I passed (yay!), what caused NO to shoot up after installing a brand new cat which helped HC drop way down? Thanks in advance! Wish me luck.