HELP!!! Only getting 6 MPG from my 500.

[CShep]

I put a fresh '76 500 in my Chevy 30 series truck. The motor is .030 over, has a Comp Extreme energy towing cam, and a Edelbrock manifold. I didn't get a carb when I bought the motor, so I swaped the Q-jet from my worn out 350 onto the 500. (I needed to get the truck running quickly) With this carb on the 350, my truck got 10-12 MPG. Now I am only getting 6-7 MPG and the Cad engine is very sluggish. The Cad motor runs hot, and the plugs are light gray/white in color. Can this Q-jet be rejetted to work correctly on the Cad? Where do I start? What kind of milage should I get in a 1 ton truck? Thanks.

[Al from MTS]

Too much gear and not enough cam would be my bet for several problems.
If you are crusing the Cad engine above 2800 RPM with a cam that has 215 or less duration @ .050 it will get por MPG. It's also going to run warm as well.
What MPH do you cruise at? What RPM @ that MPH are you turning?

[CShep]

Hi, The truck has 3.73 gears, TH 400 trans, the cam is about the same as an MTS 10. Engine runs about 2600 RPM crusing @ 60 MPH on the interstate. I have to keep a lot of throttle on it just to maintain that speed. Engine is running very lean, but is using way too much gas.

[dave_brode]

CS,

Did you degree the cam? If so, where is it? Have you done a cranking pressure test?

What does the ignition curve look like? Is it pinging any, or just lazy?
Dave