I have a friend who has flown the Fox twin carb 6.4 for about 3 years. It always started and ran good. However, when we would fly together it never seemed to have the performance that my Brison 6.4 with a single Walbro SDC80 carb did. One difference might be that the two carbs are piston ported and mine uses reed valve induction.

I never saw him do any tuning on the engine and that also may contribute to the what seemed like less performance.

The other drawback is that the engine is fine for a stick but if you want to put it in a CAP or Extra or.... then you have to put two big holes in the top of the cowl. This major uglies up the airplane. Those Bosch caps will require big holes in an Extra cowl. My Brison (CH Electronics ignition) came with shielded plug wires but no shielded caps and has never needed them.

The Fox is certainly a quality engine and if the price is right and the engine is in good shape and you want it then by all means get it.

Ken