I have a 1973 rebuilt quadrajet on my 1972 GS455 which has a mild build. Edelbrock Perfromer manifold, small/medium cam (don't know exactly) HEI Distributor, & Headers. The car runs but burns my eyes it is soooo rich. I have tried turning the two mixture screws up front with no affect. Any suggestions? Thanks, John
Look down into the 2 primaries with the engine idling. Do you see any fuel dripping from the main nozzles? If so, you may have the throttle blades open too much and you are idling on the mains. Or, the float level is too high and you have a slight flooding condition. The idle mixture screws only control the volume of mix, not the air fuel ratio, and only at idle.
I have seen cars with big cams that do not allow complete burn and cause this as well. Friends Hurst Olds does the same thing.
Do you have a PCV valve connected to the carb? Might be this, if the jetting doesnt work. I took mine out and replaced with 2 fresh air breathers, and i had the same thing happen.
I will check the primaries at idle and see if that is what is going on. Is there a way to adjust that? There is a new pcv valve hooked up so it shouldn't be that and I don't think the cam is too big. When I got the car it had a SP1 intake and a holley and it ran real strong. Wanted the ram air system back on so I swapped it all out. Thanks, John
If your initial timing isn't high enough, the throttle blades have to be opened too much to maintain an idle. This can cause the engine to idle on the mains and pull fuel from the primary nozzles (nozzle drip) This can also happen with a small blocvk carburetor on a big block. Are you sure you have a big block Q-jet? What is the number?
From the posts to date, it appears that everyone has ideas, but no one is offering checks for a fix. It is very likely that it is HC's, or wasted fuel burning your eyes. We need first to determine the cause, then formulate a solution. First, determine whether ALL of the cylinders are firing. Pulling off one plug wire at a time should affect the engine the same way, causing an equal DROP in engine rpm. If the RPM rises, you likely have a firing order issue. If the RPM does not change, you likely have a dead cylinder. If there are no individual cylinder issues, you then need to determine whether the engine is running rich or lean. It is likely running lean, and slightly lean is worse than a little rich. Try closing the choke slightly, and note the engine's reaction. If the rpm rises, you are running lean. If it drops, you are likely running rich. Try disconnecting a vacuum hose. If the RPM rises, you MAY be running rich. I suspect lean running. The cam, mated to the Q-Jet is likely causing a very lean condition. Let' s start there, and, if you like, PM me. Ray
I did manage to start it up last night and let it idle. It did look like fuel was present dripping from the venturis in to the main primaries. I will also play with some of the suggestions from Ray and see if any of those issues are there. Adam, right now, I don't think I have anything going on Sunday. Are you going to be at the meeting tonight? Thanks, John
Sounds like nozzle drip. Temporarily raise initial timing to about 14* or so. Then screw the idle speed adjustment out to close the throttle blades. Se if it is still dripping. The triple venturi on the primary side of the Q-jet is very efficient. Doesn't take much to initiate fuel flow. The throttle blades are open too much. What number carb is it?
I didn't see a carburetor number posted, or the exact engine specifications, etc. Most likely cause is that the carburetor is not correctly calibrated for the engine. It lacks sufficient fuel at the engines vacuum at idle speed, and probably not enough idle bypass air either. This requires the throttle plates to be opened far enough to pull fuel from the main boosters (nozzle drip). The cure is to recalibrate the idle curcuit in the carburetor. As soon as you set up the carburetor to add enough idle fuel you will gain control with the mixture screws and will be able to clean up the idle. Raising the timing will help as well, but is basically a "crutch" fix for insufficient idle fuel delivery. I would also add that carburetors that are lean at idle will stink a LOT worse than one that's just a tad rich. Lacking sufficient fuel in PPM for complete combustions results in LOTS of unburnt fuel coming out of the pipes, and will literally run you right out of the shop, stink your clothes up, etc......Cliff
I checked the wires and those seemed to be ok. I did slowly close the choke and the rpms did rise. So according to Ray, I am in a lean condition. So what do I do next? Thanks for the help everyone! John
I'll bring the vacuum gauge, timing light, and some other goodies tomorrow. Is Jimmy coming? I thought I heard him mention he wanted to meet up, but my beer fog was thick on Thursday night:beer
We found out that the full vacuum port on the qjet was not pulling any vacuum. I believe one of the carb gaskets is wrong. (the base plate-to-carb body gasket). We switched carbs with a known working qjet, and the car no longer has the (huge) increase in RPM's when it is choked. The smell isn't as bad, either. We tweaked the timing up a bit and backed off the idle. Has anyone had a problem with clearance issues with the HEI coil-in-cap distributor with the cap screws hitting the intake? I can't advance the timing any further, due to it hitting the intake. It's a Performer.
