The T-slot continues to feed long after the main starts, so IJ, IAB, MJ and MAB all conspire to affect the A/F.eric8 wrote: ↑Thu Apr 29, 2021 3:10 pm With 33 HSABs all around, what would be a number to start with on the primary HSAB? And if im understanding correctly, change just the primary ones, correct?
I was thinking about the cruise situation today. At 60 mph, I assume the throttle blade is past the transition slot. What is responsible for enrichment in this "window" where the throttle blade angle is increasing (i.e. beginning to accelerate up a hill), but prior to the PV's opening? Strictly the booster sensitivity? And lowering the primary side HSAB should help increase this sensitivity?
At some point in the large throttle opening range the lowest pressure in the carb moves up to the booster nozzle, in which condition the pressure is higher at the T-slot than the booster so the idle circuit reverses and the idle jet becomes an air bleed to the main well. In the part-throttle range up to significant load the T-slot continues feeding long after the main nozzle has begun to discharge so the A/F is a combination of idle/T-slot circuit and main nozzle. Keep in mind the in the mid-range both T-slot and main nozzle are metered by the restriction of the main jet because the restriction of the main jet affects the head pressure on the idle jet.
The problem with the high idle jet is because it is above float level air from the idle air bleed can easily flow back upstream of the jet orifice when intake manifold pulsations cause oscillating flow. This condition causes the fuel flow through and downstream of the high idle jet to be erratic and also causes the pressure in the main well to oscillate, resulting in erratic discharge from the main nozzle.
All this carb metering behavior of air and fuel was figured out over a hundred years ago and is reported in detail in NACA TR-49, and in fact this forum has a few descriptions of this in posts over the last decade or so.