Oz,

There are four upgrades you can provide for your OS 160 FX installation, which will greatly improve performance and the ability to utilize larger props.

1.) let the engine breath properly - Switch to the Bisson BGX 3500 Pitts Muffler, which offers a less restrictive airflow and as a side benefit has deeper sound.

Muffler: BGX 3500 Pitts (direct bolt up)
Product #: 4220

2.) stop taking pressure from the muffler for fuel flow - Switch to the VP-30 Perry Pump, it regulates the supply of fuel to your engine with no variation in pressure regardless of fuel level in the tank or its location - never to lean or rich.

3.) return to the original carb - the OS 160 carb has proven to be an effective carb.

4.) swing a greater prop load - the above setup should provide 9400 RPMs with an 18x6W Prop. I'd recommend an APC 18x10 or 19x8W or a 20x6W single blade prop. If prop clearance is a problem, you can use a three blade: 16x10, 17x8, 18x6. These larger props should provide 7800 - 8400 RPM.

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Schpankme