Gents,

My way of thinking because the name of the thread is
"Perry pumps and regulators."

The (Perry) pump
(Perry) pumps do not give you fuel injection, so you always need a metering system to get the right fuel air ratio and the carburetor ventury and sucking inlet of the engine will do that for you.

Using a (Perry) pump, you normally need less fuel sucking pressure, so to have more power you can use a greater bore, with the result less resistance of the carburetor but it still is a metering system.

Using a pump can give a better, more stabile fuel air ratio, more independent of the position of the plane and level of fuel in the tank in full power situation than without having one.

Because of the higher carburetor inlet fuel pressure when using a pump, you need a two needle carburetor to prevent the engine gets too much fuel in low power rate.

Adjustment of the pressure in midrange and optimal fuel air ratio at max does not guaranty me the optimal fuel air ratio in the mid range but only one fact, the engine does get (more than) enough.

When you cannot optimize the midrange with a Perry pump you can try to modify the characteristic of the (“low”) needle. I did it in the past for my Webra Speed 10 cc (0,60) with pipe and “standard” carburetor. Maybe this is done by Perry with their carbs.

The regulator

There were more than 2 brands (Iron Bay / Cline) of fuel pressure regulators in the past and I built them even myself for more than 30 years.

A fuel pressure regulator gives you a more optimal fuel air ratio for your engine, less or even not depending of position of the plane or level of the fuel in the tank.

When using a fuel pressure regulator you also can use a greater bore carburetor so less resistance and more power, just as with the pump.

When using a pressure regulator the inlet fuel pressure of the carburetor normally is lower than when using a pump so you have often a better fuel air ratio in the midrange and even on a lower power level than that.

You have to check if the exhaust pressure is enough to get enough inlet pressure for the pressure regulator in “nose up” position, if not, you can generate more tank pressure by using a check valve between exhaust and tank., When you use one, you have to dé-pressurize the tank after the flight or have to make a very little tiny air outlet hole between check valve and tank.

You can use crankcase pressure by using a tap on the crankshaft housing or back plate (with check valve) for the tank but you will have a lot of pressure, about 7 PSI on your tank, so be careful and think about not forget the dé pressurizing after the flight. (with a fuel tank leakage you have to drain the plane!)

My Conclusions, to make my story complete

All my points are independent of two stroke or four and even a brand, it’s important to look at fuel consumption because with a pump on a four stroke the engine maybe is as thirsty as a 2 stroke!
Last point and not technical, I think using a fuel pressure regulator is typical Dutch, because we want power for money and not a wet airplane. I use them on all my planes, see the picture.
Two regulators, one "experimental" pump/regulator like Walbro.
Walbro a brand of carburators, does show us, making a fuel air ratio is something else than making horsepowers!

Just my two cents for any drop of fuel.


Cees


Edit: Walbro description