PRESSURE IS THE MEASURE OF RESISTANCE TO FLOW
THE DEAD HEAD STYLE REGULATOR
works with a spring on a valve that allows the valve to open once the DIFFERANCE IN PRESSURE between the sides of the regulator valves fuel lines has changed
think of it as a door that has 7-10psi on the feed side and you want lets assume 5.5 psi at the carb
as the fuel pump fills the line it eventually (fractions of a second )reaches the point where theres a voluum of fuel past the valve with enought pressure to allow BOTH the SPRING and the fuel pressure past the valve to close the valve untill the fuel is reduced to the point that the SPRING and the remaining fuel pressure/voluum beyond the valve can not hold the valve closed and the valve is force open and held open untill, that diffearance in pressure is restored. now lets launch the car hard, the pump that had maintained 8-10 psi to the regulator, 5.5 psi past the valve and the spring in the regulator is now fighting the fuel in the line feeding the regulators enertia, and the sudden drop in pressure as the throttle drops full open in the carb,what the pump sees is the full 8-10 psi or MORE the regulator sees a sudden drop off to near zero and it opens wide, if the fuel pumps able too it tends to flood the fuel bowl for a second then the valve slams shut, untill the pressure drops off as you hit each gear the cycle repeats, the result is a surge in pressure and a rapid drop off in voluum then a rapid flood of fuel that rapidly cycles as you go down the track
if you had a accurate fuel pressure sensor at the carb youll see a rapidly cycling pressure/flow
if some crud gets stuck in the valve it cant close and your carb FLOODS OUT, because it must fully close every few fractions of a second to work correctly
the bye-pass regulator functions in a totally differant manor
assuming the same set-up but you replace the regulator with a bye-pass style regulator, the bye-pass regulator works by opening a valve too a much lower pressure path for the fuel to return to the tank,the open fuel return line. anytime the pressure exceeds the 5.5 psi,youve set it to, so the fuel line to the carb can only see a max at that 5.5 psi. now the pumps sitting there potenially supplying at 8-10psi just like before, but it can never exceed 5.5 psi because the bye pass regulator bleeds of any excess the pump supplies. but lets look at your launch, if the pressure drops to 6- 7 psi nothing changes at the carb, if it increases to 10 or 12 psi, nothing changes at the carb,if it drops to to 5.5 psi or less the valve to the bye pass line will close maintaining at least what the pumps suppling, but thats seldom a problem, if the sudden changes in pressure and over pressures that happen when you suddenly change the fuel flow required or the (G)loads on the system that potentially screw things up,the bye-pass regulator style regulator isolates the carb and maintains the desired 5.5 psi FAR MORE CONSISTANTLY
now lets assume the spring get weak over time or the adjustment gets set at 4 psi in error, with the bye-pass style youll probably never notice ,if you had a accurate fuel pressure sensor at the carb youll see a rock steady pressure/flow
should some crud get stuck in the valve and it cant close NOT MUCH HAPPENDS, because its normally OPEN not closed
if you check youll see MOST EFI systems are BYE-PASS regulated designs also due to control and relieability issues
but on the dead head the cycle just gets about 20% more erratic and more frequent in the cycles, further weakening the spring over time
