There are several circuits in any carburetor, power being one of them. When you step on the gas and get up to speed, more gas needs to be supplied to the venturi. This is accomplished by the power valve. The 2150 can have either a single stage power valve, or a dual stage power valve. As the throttle is opened, the engine vacuum drops and once the vacuum reaches a certain point, usually around 7.5 HG for the single stage type, the power valve will open and allow more gas to enter the venturi. For a dual stage power valve, the valve will open 1st at the high vacuum point, then at an even lower vacuum point the power valve opens even wider.
The dual stage power valve comes in many different specifications. Use the one supplied in the kit for your engine.
A single stage power valve can be used in place of a dual stage power valve and you notice very little difference in performance.
To test the 2 stage power valve you will need to apply vacuum to the power valve. This is done by connecting your vacuum test to the end of the power valve that screw into the carburetor. The trick will be finding some sort of adapter that will fit the power valve. Slowing apply vacuum. You will feel the valve move at the low end of vacuum, then at the higher end of vacuum. Keep in mind that an accurate test would require a scientific test bench, but you should get a close reading with a hand vacuum gauge.
Gas in the power valve cover:
When taking off the power valve cover, if there is any gas in the cover, then you have a problem. Either the valve is leaking, or maybe the gasket is leaking.
Be sure the gasket is centered.
If the power valve has a recess for the gasket, then the gasket must fit into the recess.
Spray the gasket on both sides with silicon spray lubricant.
Spread a thin coating of Permatex gasket maker around the edge of the gasket. Do not get any on the face of the gasket. This will help keep fuel from leaking through the gasket.