Originally Posted by Augusto
it has happened to me that sometimes q-jets never work well again, no matter what I make to them, I have several on the shelf that look brand new but they just don't work well, I think they wear out the internal passages or something like that because even after a through clean up and a new parts kit they just don't work well anymore.
stay away from the late models with the internal aneroid, they are the worst, and the electronic models just won't work, smog crap.
I firmly believe that the best improvement you can do to an old car/truck is buying a brand new carburator, I like holley's 1850 for SBC 350's
The idle tubes need to be removed. There are spaces below each one that can easily become plugged and cleaning w/o removing them is next to impossible. Because these orifices also contribute to the overall air/fuel ratio/fuel delivery, if they're not right drivability will suffer.
Once the idle tubes are removed, the passages for the idle restrictions and the idle tubes (they're next to each other in the main body casting) can be properly cleaned out.
If the idle tubes were removed carefully, they'll go back in using the original collars just fine. Otherwise, Ruggles sells replacements, both pressed (like stock) or threaded.
The aneroid type APT was a '75-only deal for the most part. There may be carbs on either side of '75 that have it, but they'll be rare.
The feedback Q-jet as used w/the CCC emissions system can be used for drag racing by removing the metering rods, then rejetting it using smaller jets w/o the metering rods. An electronic Q-jet carb set up like this will not be a good candidate for street use- just for drag racing/WOT use mainly, although it'll work well enough to get back to the pits after a run.