I've been following the injector thread for a few days so today I tried an experiment.  I ran my Renisis with stock injectors (295 Pri and 495 Sec) on the ground to see how it ran with primary or secondary injectors turned off and how much HP I could generate with the 295 cc primaries.  Note - My fuel pressure is set at 42 psi.

I found I could run around 140 HP ( HP as shown on the Not Calibrated EM-2) with the primaries on and the secondaries off.  I also found that as I opened the throttle above the 100 % duty cycle of the primaries the engine would go lean quite rapidly and quit. If I were in take-off mode at low altitude and had a secondary injector fail I don't believe I could diagnose the problem easily  and keep the engine running on the primaries!!
My theory as to why the engien quits is that as I am running only on the primaries and I advance the throttle beyond the point where the primaries are at 100% duty cycle the engine starts to go too lean and the RPM's decrease - This causes the MP to increase because the engine is pumping less air.  As the MP increases the volumn of air in the combustion chamber increases.  You need more fuel to compensate but the injector is already supplying the maximum fuel it is capable of supplying.  The fire goes out and the engine quits.
I believe to keep the engine running when I have a secondary injector fail I'd need to throttle back to some where around 18 inches MP before turning off the secondaries and figuring out the secondaries are bad.  If the engine ran smooth on the primaries I could slowly advance the throttle to increase HP as long as I did not go too high MP and get into the lean condition.  This is just too much stuff to do at low level just after take-off!!

I now plan on replacing the blue 295 CC primary injectors with yellow  495 CC secondary injectors!!

Dennis H.

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