I still think that his mileage problem is that the cam is probably radical, the carburetor isn't to big at 650 cfm's, I would go over the entire ignition system, fuel system, vacuum lines, correct timing. As I said earlier, 340's are a performance engine they wasn't designed for mileage. But I would think that a well tuned stock 340 should get mid teens anyway. I think that the compression should be checked out and see if the cam was degreed. You simply can't have a performance engine and mileage too,won't happen except for the late model high tech cars.
