This reminds me of when the Perry backplate pump / carb sets were first becomming available...mid 70's...
A friend bought one for his O.S. .60 FSR in his Kwik Fli III...(engine mounted upright)
He fiddled and fiddled with that slide valve adjustment for days...flying back and forth..upright, then inverted...burned a couple gallons...
After all that, he said that the adjustments didn't seem to make any difference...