<VV> Turbo fuel consumption problem

[Grant Young]

I have a friend who has asked what might be causing his turbocharged Corvair to be getting
very poor fuel mileage. While the first thought might be a carburetor problem, it was been
rebuilt recently and seems to work like it should - easy start, smooth idle, good acceleration
and boost and no driveability or gas fumes (rich) issues. He says he usually drives it spiritedly, 
not wanting to get things carboned up, and is getting well under 10 mpg, sometimes only 4-5. Doesn't
seem to have a leaking fuel pump either. Just checking to see if anyone has experienced similar 
issues or has recommendations on what to look for (other than Smokeys).
Thanks,
Grant