So what is a Perry Pump and what does it do?

Well, the VP-30 Perry Pump produced by Conley Precision in the USA  is a device used to regulate the flow of fuel from the fuel tank to the carburettor. It delivers an ideal .25psi to any model carburettor from a .15 to a 3.0 cu.in. engine. The pressure remains constant throughout the entire engine speed range and once the needle valves are adjusted, the mixture will not vary regardless of how low the fuel in the tank or the attitude of the helicopter, thus eliminating rich/lean mixtures.

The fuel pump is exactly the same item that is fitted to the new OS-91 SX-H PS engine seen in the pictures to the right and is used by World Champion Curtis Youngblood on his JR Vigor CS and JR Vibe models.

What is required for installation

To fit the pump to other engines such as the OS-91 SX-H Ring or OS-91 SX-H Ring C-Spec you will also require a glow fuel T-piece, a threaded fuel nipple and a VP-2CV one way check valve. The fuel pump comes with a P-clip for attaching it to a suitable place on the helicopter and also a length of red tubing to connect to the crankcase. This red tubing is much harder walled than standard fuel tubing which should not be used.

Modifying the engine and fitting the pump

Before fitting the pump the tension spring must be removed from the pump by removing the small screw and teasing out the spring with a small screwdriver or paperclip. The spring should then be carefully stretched to twice its original length before re-inserting it into the pump. Stretching the spring is to compensate for still running the muffler pressure system into the main tank.
The rear crankcase cover also needs removing from the engine. The centre of the cover should be drilled and tapped so as to fit a small fuel nipple. Take care when doing this and make sure the fitting is flush on the inside of the case before re-fitting the cover to the engine. These are the only modifications you will need to make to your engine and pump.

Plumbing it all in

Once you have modified your engine the fuel pump is then fitted and plumbed according to the diagrams shown right depending on whether or not you are using a header tank in the fuel line. Click on the diagram to enlarge. The pump has arrows on the end cap and it must be fitted with the fuel flowing through the pump  in this direction.
The pump supplies fuel from the main tank or header tank to the carburettor via a t-piece. Any excess fuel which is not used by the engine is returned from the t-piece back to the main tank via the one way check valve. Once the pump is installed the engine will run far richer than before the pump was fitted and the carburettor mixture will need to be leaned out accordingly. To check that the pump is working correctly pinch the return line to the main tank and note that the engine fuel mixture becomes much richer.
Fuel leaking from the small drain hole in the pump means that the pump diaphragm is damaged - the pump is a sealed unit and cannot be repaired. If the pump is leaking it may not supply enough fuel to the engine causing the mixture to go lean. The entire pump should be changed out of this occurs.