Peter:

What year is that 450?

Makes a difference as the eariler ones had D-Jetronic injection, later ones K- or KE-jetronic, and troubleshooting is different.

Have you done a complete tuneup yet? That is, plugs, wires if old and hard, points if you have them, timing check, mixture check and adjustment?

Very likely you have a serious rich condition -- you should get around 12 in town and 16-17 on the highway. 6 is way too low.

However, you won't get much better -- these cars were designed for power and reliability, and gas milage wasnt' much of a concern.

I'd love to get a 2.65 rear end and a four speed auto in mine....

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!