Dave may be correct, Perry.

Here is what I think could occur.  First, The oil  meter pump itself is a positive displacement pump.

Therefore, from the standpoint of the pump it will always disperse any oil fed to it into the injectors and combustion chamber under some amount of pressure.  However, the shaft opening that drives the pump also provides for the oil flow from inside the Engine Front mount into the metering pump.  There is a hole in the boss of the metering pump shaft (on the inside of the front housing) that is open to the atmosphere.

  At sea level of course this hole in the boss results in 14.7 psi of pressure on the oil in the meter shaft.  So as the positive displacement pump opens a chamber  - the oil flows into the chamber with the help of this 14.7 (or what ever the differential between the pressure in the pump chamber and the atmosphere- it will something less than 14.7 but probably greater than 12?)  and gets "squirted" toward the injectors underpressure.

Ed;

I hear what you’re sayin’, but I really don’t think so.  How much pressure does it take to make hot oil flow through a short length of tube (or a port in the pump) at a VERY low flow rate?  Very little.  We’re talking a few cc/min; and I’d guess even a couple of psi, would do the job nicely.  And at 8000 ft we still have; what, about 11 psi.

As we go to higher altitudes it is probably more likely that we’d get vapor lock upstream from the fuel pump before we stop getting oil from the metering pump.

This is just off the top of my head, so, you know, maybe there is something I overlooked.  The question is: what phenomenon was Atkins observing?  He obviously had some reason for his statement.

Al