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Old 11-23-2008, 04:24 AM
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Jetdesign
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Default RE: perry pump for OS 120 AX - does it help

I have a perry pump on a 120AX and it works great. The 120AX has a spot right on the center of the back plate that looks like it was made for mounting the pressure tap. Also, I had a problem (not related) with my AX; I sent it in with the back plate drilled out and they still honored the warranty. So, just pull off the back plate (4 screws) and mount the tap right in the center of the back plate. The pressure tap won't go all the way through the back plate, so no chance of interfering with the internal workings of the engine.

With the pump, you tune the engine so it's just off peak rpm, like 75-100 rpm just to make sure it's not lean. The plane will not lean out in the air, or at any attitude. It's really a sweet contraption.

Cover your muffler tap so you don't leak exhaust stuff everywhere, and only use the pressure from the back plate to the pump. A line goes from the tank to the pump, from the pump to the carb, and a vent is needed on the tank for ambient air to enter.

Last thing: you want your needles set from before using the pump, then tune the pump to the engine. You should have your low and high mixes set with the needles, and adjust the pump for smooth transition, and obviously slightly tweaking the needles if necessary.