MPG change, where to start looking? Options

[914Bryan]

I know this isn't an exciting high performance question, but a question just the same.

I'm having an issue with the mileage my 74 2.0 DJet and am wondering where to start looking for the problem. I commute 60 miles each way to work (120 total). My driving is 98% freeway, non rush hours so a steady 75 mph, motor is turning 3200.

I could always count on 32mpg, day in, day out. Over the last two months, it has slipped to 28mpg. I burn a tank a week, so this has been about 8 tanks of gas that I have noticed this.

Engine is running fine, no change in performance.

Would a tardy valve adjustment cause this? I'm a little over 6k since my last one.

Any ideas?

[Cupomeat]

With everyone else's advice, I'd go over the basics;
1. plugs
2. points
3. valve clearance

Now, do you have your cooling flaps and thermostat still working on the engine? If it is running too cold, the mixture will be enriched.

Now, strangely my audi 1.8t motor seems to give me the best gas mileage around 50-70deg ambient. You would think a colder temp air charge would be the most efficient, but I lose 2 MPG running in the winter, and that is a modern watercooled car.

Good luck