Hello guys, I have a 1990 mazda rx7 with a chevy 302 build swapped in, I know its not a camaro but its got a z28 motor so I hoped maybe I could get some help here. I am not very familiar with carbs and I have a few questions about tuning I would like to ask, however to begin with I have a few basic problems I am curious about. I recently installed a wideband o2 sensor in my car (so I can monitor my fuel trims and tune my carb efficiently). I am curious however if it is normal on a carbed car for the fuel mixture to go very rich when decelerating in gear. From what I've gathered this seems to be a common thing with carbs, but I'm still curious. My other more major concern for now is that when I will be cruising in gear for a while and then push the clutch in or put the car in neutral, the car will go very lean and the rpms drop to the point where the car is on the verge of killing itself. Does anybody know what could be causing this? So far I have messed with my idle mixture and set the float levels according to holley specifications. I will search harder for vacuum leaks under my hood because my idle seems to vary a little more than it used too, but does anyone else have any ideas what could cause this? I have a holley 670cfm carb by the way. Thanks guys

 

That's normal for a carburetor equipped engine to be rich on deceleration. The engine is still producing vacuum so it is still pulling air into the carb so it is also pulling fuel into the engine. If it was fuel injected it would turn off the injectors on deceleration so it would not go rich. The beauty of fuel injection at work, saving gas and producing less pollutants at the same time.
Kind of hard to diagnose a car without looking at it but it seems as if you have a timing issue instead of a carburetor problem. Advance the timing some and see if that helps. Also check to see if the advance is hooked up to the correct vacuum source. If it is an HEI distributor make sure it has vacuum at idle. Another thing to check is the power valve in the carburetor. Holley's have been notorious for blowing them out if your car back fires through the carb for any reason. Which would make it idle poorly and possibly cause the problem also. Just a starting point for you.