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!