Actually it's not unusual for the OS FX series .40 & .46 (obviously including the FXi). It was the reason that I sold all of my FXs & replaced them with TT Pro engines. It seems that the majority of dead sticks at our field occur with OS .46 FX series engines (to be fair, the majority of engines there are also OS engines).

Hobbico doesn't warrant the engine -- OS does, so bugging Hobbico won't help -- contact OS Engine.

In the mean time:

-replace all of the fuel tubing (again) including the tubing inside the tank
-ensure that the engine is firmly mounted -- check that the firewall bolts & engine mounting screws are tight
-check thsat the backplate screws are tight
-check that the cyl head screws are tight
-check that the carb o-ring is not torn & that the carb is correctly seated on the crankcase (no air leaks)
-ensure that the prop is balanced
-ensure that the crankshaft is not bent
-ensure that the needle valve o-ring, or other bits of the needle valve assemby are not loose or leaking
-ensure that both the high & low speed needles are correctly set & that the engine transitions smoothly from idle to full power

If none of this works, try mounting the needle valve assembly on the firewall, instead of on the engine.