Air-Fuel Idlle Adjustment

you made it richer.Six turns is above average.First check for a vacumn leak.if you have a leak that would explain alot of turns.you could also retard the timing a couple of degrees which will lean you out a bit.The best thing to do would be adjust your mixture and timing while at the smog station with the smog machine in test mode.most mechanics will let you do some minor tuning like this if your quick and there not too busy.good luck

If you adjust on the Smog machine, you'll find that as you lean the mixture out, hydrocarbons go down, down...then they shoot up to the moon. At some point, you lean out enough to get a single-cylinder miss, which allows that cylinder's gasoline out the tailpipe where the smog sensor is waiting. FYI, your 30+-year old Motorcraft carb is in dire need of replacement, I suggest. Few-to-no shops work on those carbs anymore, and even finding rebuild kits is not easy. What year is your Pantera? In CA, '73 and older are exempt from testing, so many '74s which were actually built in 1973, have been re-registeed as the year of build, so this nonsense goes away for them. Others apply for "Historical Auto" plates which are also somg-free.

The carburator on the car now has recently been rebuilt. Prior to the rebuilt, the car has always passed. I live in Illinois were the 72 year cars are tested at operating speed and at idle.

I was told decades ago, by an expert, that every time you "open up" a carberater, you take a chance on it NEVER working correctly again. Because they are flow calibrated at the factory. I have found this to be true in some cases. Good-Luck, Marlin.