Well it's finally running. Rough as it may be. Super. Super. Rich. How do I tune with a dwell? Can I use a multeter? Bench settings for the (and forgive me if I'm using the wrong names) lean mixture solenoid screw and the enrichment screw(? The big *** one in the center on top) when I say rich... I mean my gas car acts like a diesel.

 

First off, understand that the electronic carb system itself, working properly, has relatively little "authority" over the mixture. It's not like EFI, where the control system has literally a 20:1 or greater "dynamic range". The CCC system, working properly, only has about a 1.3:1 range, IF THAT.

Furthermore, the whole thing is designed in such a way that, working properly, almost any error that it makes, is in the lean direction. It was designed that way for emissions compliance. Which is to say that, working properly, it can create a condition where there's MAYBE 1.1 times as much fuel as the engine needs (let's say, enough to take the mixture from 14.7:1 at cruise, to 13.2:1); BUTT, it can take it a factor of maybe 1.2 THE OTHER WAY, toward lean; to maybe 19:1. There's NO WAY, working properly, that it can make the car particularly rich.

Key to the whole thing here is working properly. That begins with fuel feed control. That means fuel pressure, first and foremost. It's common to see people think that more fuel pressure is better, because that's what they're accustomed to with EFI. IT'S NOT. If your fuel system could keep your carb's bowls full at .001 psi of fuel pressure, then .001 psi would be all you'd need. That's too extreme to be literally true of course, but the point remains: you only need enough fuel pressure to keep the bowls full. With a Q-Jet and a small block, the MOST fuel pressure you would EVER need for that, is around 5 psi; and that would be ONLY at 7000 RPM and beyond in a 400. It MIGHT take 5.5 psi to force enough fuel past the needle valve under those circumstances. For a 305 at idle, 1 psi at the needle valve would be PLENTY. Bottom line, check your fuel pressure control system, if it's not just a straight-up block-mounted mechanical pump and a sock in the tank. If you have ANY kind of electric pump ANYWHERE in the system, you probably need to regulate your fuel pressure DOWN.

Next most likely problems are: corroded fuel bowl around the needle valve allowing fuel to bypass it, and corroded fuel bowl around the metering well plugs at the bottom of the fuel bowl. Note the common thread here of CORROSION. The fuel bowl is chinesium of some sort (basically, the cheeeeepest thing they can find that won't dissolve in gasoline), and those other parts are some other metal. 2 dissimilar metals immersed in a conductive fluid, make a battery, which then erodes one of the 2 metals. In this case, the needle valve is brass, and the plugs in the bottom of the bowl are aluminum. Both will literally EAT the chinesium over time in the presence of moisture. Needless to say, if the fuel bowl is directly exposed to manifold vacuum, or the needle valve can't shut the fuel off when the bowl is full and the fuel overflows into the throttle bores, you have NO CHANCE WHATSOEVER of ever getting it to run right.

Your fuel system or carb is DEFECTIVE in some way. All the messing around you can do with "tuning" activities like bench settings or dinking with the IAB (idle air bleed) valve will accomplish EXACTLY NOTHING until the defects are repaired. Based on your description of what's going on, you're a long way from doing any "tuning" just yet.



Check your fuel pressure and fuel level first. No more than 5 psi EVER, and the level should be about 3/16" from the top of the bowl with the float hinge pin fully held down. Epoxy over the plugs numbered 3 & 4 in the bottom of the fuel bowl in the photo; 1 & 2 aren't a problem, and 5 & 6 are outside of the carb and will leak on top of the intake but not into the engine but you should probably do the same to them anyway. Wire-brush them down to clean shiny uncorroded metal, sterilize them with lacquer thinner or MEK or acetone NOT brake cleaner, paint thinner or electric motor degreaser, glop them over real good with JB Weld that has the steel powder, bake them in the oven for acoupla hours at a low temp like 180° or so. See where getting those things right takes you, and once you have achieved control of the fuel, you might be ready to try "tuning" on it.

 

Still always consistently excellent helpful detailed info here on TGO.

 

I have built probably 75 quadrajets and 25 dual jets manufactured from about 1977 into the 90s. I have NEVER seen a fuel bowl corrode during normal use nor have I seen a well plug leak with the newer plug style. It is much more likely that the needle and seat are simply worn beyond having a good seal, the float is deteriorated or fuel logged or even that the mixture control solenoid has failed. Finally I see the most issue with dirt from neglecting to change the fuel filter or air filter or even running without an air filter or fuel filter. The newer q-jet fuel bowls are plated and it tends to create minor corrosion of the plating and not hurt the actual metal.