Bleeders are designed to relieve the excess air pressure build up due to the normal heating of tires. Proper setting of relief valves is paramount to their function. Loosening the jamb nut and turning the cap is all it takes to make an adjustment. A tighter cap will allow for higher pressures where as a looser setting on the cap will allow for a lower pressure setting.
Consistency is the key when setting the bleeders. Making the adjustments the same way each time will increase your relative accuracy and make adjustments more reliable. When making adjustments it is best to set the tire pressure about 3-4 pounds higher than the desired pressure. Setting the tire at a higher pressure will allow you to loosen the cap until you hear a maximum flow of air. Next, you slowly turn the cap until the air completely stops. You can then fine-tune the cap adjustment until you are at the desired pressure. By allowing the air to free flow out and then slowly tightening the cap you reduce the chance of improperly setting the pressure due to variables such as dirt or liquid on the seal.
To get a visual look at when the air has completely stopped coming out of the bleeder you can spray a small amount of Windex glass cleaner on the opening to see when the bubbles stop. Even small amounts of air flowing out of the valve will lower your pressures on the track so be sure to be precise when setting the valve. Hearing air flow at the racetrack can be difficult due to all the engine noise so a visual look is very helpful.
Maintenance of your bleeders is very important to allow you to get consistent settings. If you regularly maintain the valves then simply cleaning the seat and poppet seal with a clean damp rag is sufficient. Avoid the use of cleaners that can damage the rubber seal. Look for a factory installed screen to keep dirt and debris from entering the valve from the inside of the tire.
Inspect the spring for squareness and be sure the ends are free of burrs. File off any burrs. It can be helpful to use a very small amount of white grease or graphite on the ends of the springs to assist in getting repeatable settings. Be sure to wipe off any excess.
Some people keep a supply of bleeders in their tool box that are marked at a preset pressure so that they can plug them into a Quick Change Adaptor with assurance of a correctly set valve. For last minute changes the Quick Change Adaptor makes for a nice benefit. Setting tools and Quick Change Adaptors can be used to assist in presetting but you can also set the valves right on the wheel.
If you need the valve to hold higher pressures, be sure to use the shim that is provided. Stretching the spring is never a good idea. Bleeder springs are manufactured to be true and square. Stretching them distorts and bends the spring making the operation of the valve very unpredictable as the out of shape spring rotates and moves the poppet off center on the seat.
Consistency and proper bleeder maintenance will provide you with more consistent stagger and tire pressures allowing you to start races at full pressure so that you can race confidently into the first turn.