(Yes, I have searched, and have read the faq, including the all-important Stirling's Idle Set Instructions...)

So, the car is running after a thorough carb rebuild, and not running terribly... but I am trying to prep for smog check, so of course getting the idle fined down is crucial.

A funny thing happened on the way...

The car started fine with the "book" settings for the Air Adjust Screw (AAS) and the Mix Adjust Screw (MAS), of 2 out and 3 out respectively. The idle was high and a bit lumpy, but it would run up and down on the throttle OK, and it did not afterburn on deceleration. Very driveable. Exhaust actually smelled very light.

I started working thru the adjusting procedure in the Carb manual: warm up fully, gas cap off, idle compensator port plugged. I was able to use the AAS to get the idle down to 750 without issue, though it would stumble just a touch until I started to turn in the MAS.

As I wound the MAS clockwise, it took a considerable amount of turning to reach a point where the engine would stumble... more than one turn.

Once I finally got it to the stumble point, I backed it out a half-turn, re-centered the idle with the AAS, and re-checked the MAS.

So, It should be right, according to the procedure.

But now, the exhaust smells much worse, and the car afterburns (backfires) toward the end of deceleration.

Naturally, I don't have any access to and exhaust gas analyzer other than my nose... but it smells rich to me.

Any advice? Why would following the adjust procedure make it seem to run worse.

 

Ive been having this same issue for the past year. I rebuilt the carb and STILL have the same issues.

Next on my list; air/fuel sensor and reader.

Hello $200.

 

If your turning the needles in, your leaning out the fuel mixture... even if it does smell rich. Mine use to afterburn a little with the stock exhaust under decel. It passed emissions too.

 

Interesting. I just hate the idea of paying for a pre-test to find out if I'm right. I wish someone rented out EGAs, but I've been searching without finding a place that does.

I'm betting one hour with a sniffer could save me a ton of fiddling. But I haven't any.

 

Just go get it tested. if its running on the idle circuit then it wont run so rich as to fail the test. If all your emissions equipment is working then it should pass no problem.