1968 Firebird 350 with small cam (specs unknown) however it idles in gear without the need for a stall converter. Stock cast iron intake, factory exhaust manifolds, HEI distributor (advance unknown) initial timing at 15 degrees with manifold vacuum to the advance can. This quadrajet has a number that reveals it originally came on a 1968 Olds 400 engine. I sent the carb to a well respected Pontiac carb guy for rebuild. He installed .071 jets, replaced primary throttle shaft, and replaced everything typically done in a basic overhaul. It now runs better however it is pig rich as it was before. Wondering what to try next. It stinks up the garage and my clothes. Any suggestions, advice, and criticisms are appreciated.
Have you tried adjusting the idle mixture (2 screws under the fuel inlet)? If not, with the engine off run them all the way in to the stop (don't over do it), then back them out 2 1/2 turns each. Start the engine and warm it up, then connect a vacuum gauge and adjust the screws one at a time (slowly and not too much each attempt) until your get the maximum vacuum at idle. You may have to adjust the idle stop screw as well.
Also, do you have ported vacuum to the advance can, or is it direct manifold? I like to use direct manifold, runs a bit better that way.
Next disconnect the vacuum can and see what your initial timing is. Adjust to 17° to start with. Pontiacs like a lot of intial timing. Your total should come in somewhere in the mid 30's at about 2200 rpm with the vacuum connected.
As far as those jets, I think I have .069's in mine with a Qjet off of a '69 Buick 430.
Thanks. My next attempt is to increase the timing from 15 to 18-20. I’m running live manifold vacuum to the advance. The mixture screws are currently at 2 1/2 from seated. I’ll adjust with a vacuum gauge and a tach if I can figure how to attach it to the GM HEI distributor. First, getting the rich idle squared away then ensuring the total ignition advance is as you’ve described. My gut fear is I’ve paid to have a junk carb overhauled and have seen no benefits. I’ve owned this Firebird for two weeks and really wanted to drive it some but of course I can’t when it gases me in the process. I have to shuck my clothes in the garage and go straight to the shower after tinkering with it because of the fumes. I wished I had a plan B for another carburetor but have no idea what carbs are consistently proven as quality remanufactured etc. The Holley spreadbore (don’t condemn me) is at least a new carb, with warranty, and will bolt to my intake but it’s close to $800. Hopefully more adjustments will take care of this but being realistic and planning for the worst….
how much vacuum does the engine have at idle? Is the HEI getting at least a full 12 volts ? if you cant get a clean idle with 15-20 degrees initial timing then something is wrong.
15 in at idle vacuum. Yes solid 12 volts to the distributor. Agree that something is wrong. This site is all but dead? Is there only one person in the United States that has any experience with Quadrajet carburetors? Cliff? Is everyone now running fuel injection, Holley, or Edelbrock carburetors?
I think if you are not actually working on a Firebird, this site is asleep at the wheel. But it is still a great source of information. Quadrajets are terrific carbs, but few still know how to work on them.
15" vacuum is much too low. #71 jets are not too rich, but may be a bit much for a tame 350. The HP 350 and 400/428 used #72 and #73 jets. Depending on the cam, #69's may be better if it is really a small cam. But at idle, jets and metering rods are not a concern. The idle circuit is controlled by air bleeds and the idle mixture screws. Do as Dr. Driveability suggested. A vacuum gauge is your friend. I prefer ported vacuum for the distributor. The ported vs manifold argument has been going on forever. In my experience, ported is best for stock engines. Manifold vacuum helps when the cam is so radical it won't idle at all.
Stock timing is 9° so by using 15° plus manifold vacuum, you are way over timed. Try the 9° and ported vacuum. Adjust the idle speed screw for 600 to 800 rpm, then adjust your mixture screws to get the highest vacuum reading. As you lean out the idle, it will speed up, so reduce the idle with the idle speed screw and re-adjust the mixture screws. Keep doing this until you get at least 20 " vacuum at around 650-700 rpm.
If still pig rich, all I can think of is the float level. Every Q-jet has a specific float level that works best for that particular engine. Using a generic level like 1/4" on every carb leads to problems, yet some re-builders still do that. The plastic float can absorb fuel and sink the float. The alcohol in today's gas just makes that worse. Because of that I am back to using the old fashioned brass floats. Also, being an Olds 400 carb, there may be small internal differences that are affecting the way it runs. I remember wasting many hours on a Buick 350 carb that would not idle right on a Pontiac 400. Finding a correct year Pontiac 400 carb did the trick.
Here is another thing I ran across many moons go. I was using a fuel pump that was for a recirculating fuel system on a car that was not equipped for that. The recirculating system pump has three fittings: fuel in from tank/ fuel out to carb/ and excess fuel back to tank. This was initially used mostly on AC equipped cars to provide cool fresh fuel and defeat vapor lock. Later, all carbureted cars used this system as well as the charcoal canister vapor collector. Our first gen cars used a two fitting pump. Fuel in from tank/ fuel out to carb. Often, when someone needs a fuel pump and can't find a two fitting pump, they just use a more common three fitting pump. They just plug the return line fitting and call it a day. It works at all speeds except at idle. The extra fuel has no place to go. So it overwhelms the carb float, flooding the carb. Not by much, but enough to cause a very rich idle that can't be otherwise explained. The way I cure this is to use a three way "T" right at the fuel pump. [3/8-1/4-3/8] Then the return fuel line extra fuel goes right back to the fuel from tank line. Take a peek at your fuel pump and make sure you have the right one.
