Mazda Repair: failed emission inspection, thermal reactor, air control valve

Question
Hi. I am the original owner of a  1979 Rx7, 114,000miles. I can no longer
pass emission inspection which is a prerequisite to licensing a car in
Memphis, Tn. It failes both hydrocarbons(300%) and carbon monoxide
(slightly) standards. 4 years ago it developed a vacuum leak that my mechanic
at the time thought was do to a bad air control valve and plugged it. Prior to
this it would stall below 2000rpm. Last year a different mechanic rebuilt the
carburator and it has not passed inspection since. It has smoked at start up
for the past 5 years but it seems to drive very well and it has as much power
now as when new. The car is totally stock.  Thankyou for your help.

Answer
There are a couple of reasons why your mechanic should not have plugged the air control valve (acv). First, unlike 81 and later Rx7s, the acv on your car directs air to the outer chamber of the thermal reactor. The thermal reactor is basically an exhaust manifold with an inner and an outer chamber. If air is not directed to this outer chamber, then the reactor will overheat and start to crack. Not good. Also, you will never be able to pass emissions with a plugged acv. It sounds like your mechanic has redirected air to the thermal reactor all the time. This sounds like it was working, but it's really not the right way for the exhaust to work, and I'm a little surprised that it passed emissions this way.

As for the carb rebuild, it is possible for the carb to be rebuilt incorrectly, but it would probably not run right if it were built wrong. Why was it rebuilt? Was it leaking?

Don't worry about the smoke. A little smoke on start-up is fairly normal for rotary with a few miles on it. Your motor is probably fine, and this initial bit of smoking should not cause the car to fail emissions.

If at all possible, find a mechanic who is intimately familiar with 1st gen rx7s. It would be particularly helpful to find one that is familiar with 79-80 cars. Get the acv hooked up properly and have the carb rebuilt properly. With a decent functioning intake and exhaust, you should have no trouble passing emissions.