Eddy mechanical fuel pump

The fully warmed up and properly operating engine, will idle a long time on whatever fuel is in the bowls; perhaps 1.5 minutes or more.
For a preliminary test I stick a tiny funnel into the vent stack, and keep a 500ml bottle of 4% mixed 2-cycle gas nearby. Then redirect the pump output into a clear 2-liter pop bottle, with a clear hose, that I put on the bottom of the bottle, and then I start her up. This is a preliminary so I'm not real interested in quantity yet, so much as color and freedom from water and bubbles.
If it ain't clear I fix that. And if it has air bubbles or water in it, then I go fix that first.And if the engine idle speed changes, I dribble some gas into the float-bowl, thru that vent, before it stalls. But the hose stays submerged in the bottom of the bottle at all times.
If you had a lot of fixing to do, it now may be that the pump is filling up your pop-bottle likidy split, so perhaps the volume test can be skipped.
If there was nothing to fix, Well then, you have to do the test.
The FSM test is done at something like 500 rpm, but good luck with that.
Fill the bowl and make level mark on the bottle, then start her up and run her for 60 seconds noting the rpm, then shut her off, and measure the quantity of fuel down to the mark you made. If the engine runs outta gas before the minute is up , make a note of the time it ran.This test does not have to be dead nuts accurate because the pump is rated at near triple what a 400hp engine needs.
Then you can extrapolate your finding to whatever rpm you want, and probably be close enough.
Worst case; the engine stalled at 39 seconds and pumped whatever measure of fuel . You need to convert that to a 15 second spec so this would be 39/60 , times the amount pumped, then divided by 4; right? Ok then moving on;
Say she was idling at 800rpm and your engine revs to 5600 Then 5600/800=7 to 1, and so your output needs to be about 1/7, of the formerly estimated ~18 oz in 15 seconds. If you get double or more than that, then there's no point in trying to be any more accurate , yur done.
But if your pump is skimming the requirement, or worse, then it's getting serious.
I'm a lil muddy in the head today, so if this seems muddy to you, then just PM me or perhaps someone else will jump in with clearer words.