HotRodFiend

ok i have a 305 on an 85 camaro. with a rochester quadrajet. it idles poorly and lunges when you put it in drive. im pretty sure it has something to do with the carb. i have adjusted the idle and timing to emissions specs. im wondering if there is another easy adjustment or maybe something is gunked up causing a problem. i feel as if the engine does not get its full potential under normal driving conditions. the smog guy told me my mixture was too lean. has anyone else had this problem. any ideas?

84elco231

You didn't mention if you're running a CCC feedback system still, I assume it is. Anyway, you'll need the toolkit with instructions to set that thing up properly during a rebuild(if you do) I forget the maker of the kit right now but can look it up if you need. So here's my story: I've got an 84 CCC with the buick 3.8 liter series 1 and a dualjet e2me that had the same lean idle with a replacement aftermarket o2 sensor (I blame o2 sensor: no access to original GM 02 sensor, discontinued thus no reference). From my experimentation, it seems the computer always tries to keep the idle mixture too far on the lean side with the new sensor, I think b/c the newer sensors are calibrated differently, or the new sensors are faster than the original sensors were. Although there were multiple other issues which I can go into, the last one to resolve was the idle was too lean causing rough idle and occasional miss which the computer interpreted as a rich condition b/c the fuel was unburned, thus computer would lean the mixture even more, leading to an engine stall). So, what I did was adjust the carb idle mixture to the rich end of the range by using the two mixture screws in the carb base (the mixture screws that are inaccessible until you remove the tamper proof plugs, I used a dremel bit for this. Some people remove the cover rivets on the carb horn and adjust the air bleed valve but I wanted to adjust the mixture circuit in the carb base), so that my dwell meter connected to the green connector off the carb mixture control solenoid was showing a long dwell (1/2 scale around ~25* Dwell of 6 cylinder scale is normal range on all CCC/carb system) and thus the computer could no longer control the mixture too far to the lean side which was leading to a lean mixture stall condition. So now at idle, my dwell meter needle oscillates at the extreme high end of the range, but still oscillates, as it should (the oscillation of carburetor mixture control solenoid dwell indicates 02 sensor lean/rich crossover, a longer dwell results as the control solenoid is held on in the closed, or down position, for a longer period of time) The mixture control solenoid dwell needs to oscillate, usually mid scale, not peg to one extreme or the other of the range of throttle, otherwise if the computer cannot control the mixture (in the case of either the mixture being on one side of too lean or too rich) for a period of time, it will eventually generate a rich/lean fault code. My idle stall problem was resolved, the mixture control solenoid dwell oscillates at the high end of the scale during idle and by opening the mixture, the carb can no longer go lean enough to cause a lean stall. During part throttle (not WOT), the mixture control solenoid still oscillates mid scale as it should, indicating a balanced air/fuel ratio with normal rich/lean crossovers. So the computer is still happy, and so am I now. Don't forget to check your other sensors too (before making carb adjustments), such as manifold air pressure sensor and throttle position sensor. The throttle position sensor is in the carb body just beneath and actuated by the accelerator pump lever, with about 0.85 volts output at idle to something less than 5 (mine's around 4.4, I think) volts at WOT. Otherwise the computer won't know where the throttle is. Check for normal stuff too! Check ALL your vacuum lines for cracks, including the PCV and power brake diaphragm, the vacuum line to your manifold air pressure sensor. All this stuff needs to be in place and working properly, the egr valve should be functioning properly(ie: if stuck open with carbon particles, egr will just be a vacuum leak and destroy idle quality. Good Luck!