I have built a crude flow test bench using a fabricated box to adapt my 7043240 to my leaf blower. It flows about 450 cfm, and with the primaries closed and secondary butterflies zip tied open, provides a relatively close approximation of a flow bench. I wanted to measure the secondary vacuum draw as a function of the rear air door opening ( my carb has an adjustable stop screw with the stop ground down). The carb is instrumented to provide the vacuum depression present in the secondary main wells by 2 tubes sealed to the jet discs in the floor of the bowl, and the secondary air bleed/emulsion tubes soldered shut. I have both a digital and home made water manometer to measure vacuum. The door measurement method is the one depicted in Cliff's book.
The blower is powered by an adjustable regulated power supply although I did not adjust it for flow or depression across the carb as the door was varied so bear that in mind. The blower is not a positive displacement pump.
The graph shows the recorded pressures and surprisingly the vacuum does not drop off very much and drops only when the door is almost vertical. The drop due to the door closing I believe is a limitation of my setup; the velocity has slowed and I did not adjust to maintain constant flow.
I do realize the door will be close to the discharge nozzles when open that much but I have scarf cut mine on the bottom to allow plenty of room for the emulsified mixture to escape. BTW, my engine made 590 HP/ 608 ft lbs on the last dyno test. I plan to resume testing and air door vs hp will be tested.
