Somebody mentioned they thought the oil injection pump was not a pump at all
 but just a metering device that relied on engine oil pressure.

 Not the case. The oil injection pump is indeed a pump and is gravity fed
with oil at
 atmospheric pressure. The pumping action comes from the fact that the
plunger
 moves up and down in its bore as shown in this drawing from the Mazda book
 called "Rotary Engine". The stroke of this up and down motion hence the
amount of
 oil injected is controlled by the throttle opening linkage.

 The mechanical  pump is an off the shelf motor cycle part bought out by
Mazda.
 As I recall it is made by Mikuni.

 Paul Lamar

The pump may indeed be a pump, but in my 91' turbo it is not gravity fed, but
uses oil pressure.  There is a small passage in the front cover that gets
pressurized oil from the front housing and routes it around the front to feed
the pump.

In fact, I am very glad you mentioned this because I am about to put my
engine back together and have forgotten to adequately block this passage
after removing the metering pump.  In Bruce's video, there is a brief clip
where he reminds you to make a provision for this passage if you are using
form-a-gasket on the front cover instead of a real gasket.

I suspect that the metering pump is just that, a meter and a pump.

Dave Leonard

I just took my front cover apart and the shaft out and it is indeed gravity feed.
The pressure is relieved by the hole with the little roll pin and a turned down
section of the shaft. Oil is then fed to the pump by capillary action along 
the shaft. The roll pin is placed in there to act as a restriction feeding
the shaft with a tiny bit of pressure. A lot depends on the meaning of is :-).

I will have pictures shortly.

I suggest taking the shaft out and plugging the oil gallery with a short
piece of aluminum rod. Slightly more oil flow to the bearings slightly 
less weight and slightly more HP.
 
Paul Lamar
 
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