Common carb on early 80's 4 banger rice. Darn thing idles with the mix screw turned all the way in. Its an NOS carb with maybe 1000 miles on it, but no idle baseline settings can be found. the vacuum readings can be altered with the mix screw from a nasty 14 to a decent 20 inches vacuum but Im afraid the screw out to get the 20 is failing my low speed smog results They test at 15 and 25, 25 is fine, the 15 is about 10% over fail. The 20 is about 2-2.5 turns out. Will have to look at my old shaft leaking spare to see if the idle transfer holes are barely under the plates like a Holley.Yeah this looks like it could be a Tport sync issue;ie the butterfly is too far up the transfer port. Also the distributor advance is hooked to ported vacuum, does that sound right?To me it does. The only vacuum hose diagram shows the distributor vacuum going into the carb at butterfly level or slightly below,Hopefully above but when I put a gauge on it, I get nothing at idleCorrect until I blip he throttle,bring the rpm up to cruising rpm to see what it does then I get some movement. One more thing: I got an inline vacuum metering device in the hose to the distributor and it has an arrow on it. Does arrow point toward the vacuum source or distributor? Its called a timed vacuum modulator, sort of a one way check valve with a slow leak. Supposed to help NOx by easing off the advance when you go off the gas, Im thinking the vacuum source must pull, then when it stops, the check valve holds the advance pod vacuum for 7-10 more seconds? the BIG-Three all used similar devices at one time or another; sometimes one way sometimes the other. Do whatever it takes to get certified, then pitch it..
