[Ptero]

Yeah, the middle seventies were nightmare years for the manufacturers in trying to comply with the new emissions regs. They mostly worked out kludges and emission tech didn't get sophisticated until the 90s. A huge problem today is where people who didn't understand the purpose or effects of smog control systems went in with tools flying and screwed everything up.

I recently purchased an F800 boom truck on the east coast and brought it back to California. It had been stripped of its emissions equipment and the yahoos had installed an Edelbrock 4-barrel carb on it. It got 5 miles per gallon.

I was told by so-called experts that it would be impossible to refit the smog system, but I've done it before on other vehicles. To get it registered, I installed twin air pumps, an OEM carb, air injection manifolds and new emissions valves. That doubled the mileage and made the truck marketable in California - which added around $20,000 to its value. So don't believe everything you hear about stripping out smog equipment to get better performance.

One of the worst things people do is stick a sucking, hissing vacuum hose in the wrong place. That brings the idle up and they think they solved the problem but what they actually did is disable the vacuum advance for their distributor. Then they fiddle with the idle screw to try to make up for the loss of power by running over-rich. This gives more power at throttle but it kills their mileage and their idle stinks of raw fuel.

There is often a temnperature-controled vacuum distribution valve somewhere on the water jacket with several nipples. If you get those vacuum lines mixed up, your distributor won't advance properly and you can cut your mileage in half. I suspect you have several simple-to-fix goof-ups that are compounding the problem.

The best way to approach this is to read the general discussion of emissions controls in a 70s-era Chilton manual. They're really not that complicated in theory, and once you get an understanding of the three basic systems - exhaust gas recirculation, air injection and temperature-controlled timing advance - things start to make sense real fast across a wide range of engines.

I'm not trying to say that you can't get better performance by bypassing emissions controls. I am saying that you absolutely have to know what you are doing - and why - to get a real benefit.