Inliners International Forums General Discussion Engines dist vac advance

I'm getting about 10mpg from my 250 with headers and electronic ignition. It's in a '68 C-10 1/2 ton with 3.73 gears and a 3 speed. I don't know what's wrong. She runs good. I only see one port on the carb and it's maifold vacuum. The only thing is, it doesn't advance the timing. I can get 20 inches of maifold vacuum from the manifold, but the vacuum from the dizzy's port seems really weak. I'm at a loss. BTW, that figure is mostly highway driving (70mph @ 3300rpm) with proper warm-up, not gassing it, tailgate down, with a one barrel. Base timing is at 8-9 degrees advance with the dizzy recurved. Any guesses.

I've always been told to hook the vacuum advance to ported vacuum. That's how I had it hooked up on my 327. I'd do it the same way now if I could. Thanks for any help, and I hope I'm not hijacking the post. John.