Yes 8 mins would be about right

Remember More Power = More Fuel !!!

I have a Old OS 60 Vintage goldhead in a Jensen Ugly stick it Sucks 16oz of fuel in about 12 Mins Flat out !!! It is not all that powerfull an engine but has enough for the Ugly Stick , older engines are also less Efficent

Also Using a Tuned pipe will also use more Fuel same thing More Power = More Fuel

Putting the restrictor in the carb will just reduce the power, It would be simpler to trim the throttle on the radio so you have a bit less than full power this
would acheve the same result and if you want you could set a switch on most computer radios to override the trim for extra POWER

If the engine is running nice leave the 7D alone.

Johnkpap