Once you have your nitrous system installed, you must test the system to ensure adequate nitrous and fuel flow if you have a wet system. And then tune the NOS system. This will ensure proper performance and reliability.
Testing NOS Systems
On a wet system, start by ensuring that the fuel line is properly attached to the fuel solenoid and turn the fuel pump on. You can do this by turning the ignition key to the ACC position. Check for fuel leaks where you tapped into the stock fuel line and where the fuel line feeds into the fuel solenoid. If there are any fuel leaks, fix them and check again for leaks. You can disconnect the fuel line from the nitrous injector once you have no leaks. Then, activate the system and check for fuel flow when the system is activated, and that the fuel stops flowing when you deactivate the system. If you don't get fuel flow, check that the fuel solenoid is operating properly — you should hear an audible click when the solenoid is activated; check that you have fuel flow at the fuel filter; and ensure that fuel line is not kinked, twisted or bent. If you do have fuel flow, turn the vehicle's ignition off and properly secure the fuel line to the nitrous injector.
Now open the release valve on the nitrous tank check for signs of frost along the nitrous feed line. The frost will indicate a nitrous leak. If you find any leaks, close the release valve on the nitrous tank and fix the leaks. Open the release valve again and ensure that you've fixed all nitrous leaks. Then disconnect the nitrous line from the nitrous injector. Activate the system and check for liquid nitrous flow when the system is activated, and that the nitrous stops flowing when you deactivate the system. If you don't get nitrous flow, check that the nitrous solenoid is operating properly; and ensure that nitrous line is not kinked, twisted or bent. If you do have nitrous flow, you can properly secure the nitrous line to the nitrous injector.
Tuning NOS Systems
Nitrous tuning is another simple procedure but you should first tune your engine without nitrous as you will be running without nitrous for most of the time. Tuning the nitrous system is quite straight forward — you start with the jet sizes recommended by the manufacturer of your nitrous system and gradually adjust the jet sizes until the air/fuel mixture added by the nitrous system is perfect.
So install the metering jet of the size recommended by the manufacturer of your nitrous system. This will be conservative and will err on the rich side (i.e., too much fuel), which is the safe side to err on. Run you engine for a while with the nitrous activated and then check each of your spark plugs to determine how the air/fuel mixture is burning. The correct air/fuel mixture will produce a brownish, grayish-tan color on the spark plugs. If the spark plugs have a sooty, black color, your air/fuel mixture is too rich and you should increase the nitrous jet to the next jet size. If the metal part of the spark plugs displays a bluish or rainbow coloration, go to a smaller nitrous jet size immediately. Repeat this test until your spark plugs display the correct color. Never jump up by more than one jet size on the nitrous side and never try to work your way down from a lean mixture — that's just looking for trouble and major engine damage. You can make more power by increasing the fuel jet size and then adjusting the nitrous jet size up until your spark plugs display the correct color again. Check out page on reading spark plugs for more details on the correct coloration of the spark plugs.
You may also need to adjust your ignition timing as nitrous oxide makes the air/fuel mixture burn much faster than normal. Retard the ignition timing by 2° increments (i.e., less advance before TDC) until you feel a noticeable loss of power. Then advance the ignition timing by 2°.
Now that that's done, your nitrous system is installed, tested and tuned; all that's left is for you to enjoy responsibly — always enjoy power responsibly!