I bought one of those cheap eBay Chinese Raptor 660 petcocks for $9.95 before I knew better. It has the plastic fuel tubes instead of the brass ones and the fuel outlet nipple is smaller at 1/4" instead of 5/16" as it should be. Then I got advised of my error by some members. Well, since I had it I might as well try it out.

Here are the results:

I have a 97mm Big Bore Kit, a Mikuni VM36 carb, a Web high lift cam and a ported cylinder head on it.

I thought it would starve for fuel at high RPM since the fuel outlet nipple is smaller (1/4") than the OEM petcock or the CORRECT Raptor 660 petcock (5/16")

I have a 210 main jet, much larger than the OEM carb has.

To my great surprise it works just fine.

Sustained (for over 2 miles) running at 95 mph and NO fuel starvation problem!!  

Don't understand why the OEM & Raptor fuel nipple has to be 5/16" since that is the size fuel line I had on my Ford pickup with a 302 V8!  

Yep....Gravity system.  Super Thumper......since you have an O2 sensor....watch what happens when you are cruising along and the fuel level gets close to the "reserve".  I was on the interstate cruising along at 65 mph and saw my mixture going lean.  I switched the petcock to reserve and my mixture went back to normal.  The fuel flow rate will slow down as the tank level drops.....long before the engine becomes lean enough to stop running and let you know that it is time for the switch to reserve.

Good point Dave...I will try that to see how lean it gets and post the results here with some A/F numbers.