adjustin a quadrajet?

Question

mines runnin to lean, the small screws down in the corners, if your standin in the front of the truck, which side is the fuel? it needs just a little more fuel, doing that will I have to bring the air up a bit to?

Answer 1

I own a shop, and have built a quadra-jet in the dark in front of my headlights so I could drag race. There is adjustments on these carburetors that most mechanics don't even know are there. Standing in front of the vehicle, neither one is a fuel adjustment! They are both for air. If the carburetor is starving for fuel, then you may want to look at your fuel pump pressure as it should be around 6-8 pounds. I would say the float level is too low if it is not getting enough fuel. I see you didn't go by what I posted in my answer, and now you still can't get it to run right because you listened to a wrong answer. Sorry, but you did. Your problem is; it still back fires through the carburetor, right? The big door that opens in the back of the carburetor when you smack it to the floor must be adjusted to open at the proper rate, and the two screws you are refering to are idle control screws, and ONLY control the idle circuit of the carburetor. A vacuum chamber meters the opening of this door, but the rate is adjusted with a tiny screw driver, and an allen type wrench. This big door rarely ever opens all the way up due to the fact it can supply more air than the engine will need even at wide open throttle. You say you need more fuel, well... what about less air? Would this not be the same thing? Adjust the air screws as I instructed with a vacuum gage. If you will go to www.carburetion.com/
you will find a wealth of information. This is a company that I order all my jets, rods, and parts for all quadra-jets that I build for customers from. There is a technical section that should explain everything you would ever need to know about these carbs. It would be wise to realize many people on here that answer questions don't know what they are talking about, and/or are just after the points. You can get a lot of bad information, and it is up to you to weed out the bad ones. Pull out a couple of spark plugs, and look at them. What do they look like? This will tell you what your carb/engine is doing, and what needs to be done to correct it. Most all repair manuals has a chart that you can use to determine the problem with your engine by comparing your plugs to the plugs in the pictures. Don't assume you have a lean mixture problem, make sure. Set your float level at 3/8'' and no less. This ought to give you all the fuel you will need. When you give up, and can't get it running right, I will tell you how to adjust the big flap. If you are not going to use my information, then I am wasting my time on typing, and will stop answering your questions. I don't care about the points, I'm here to help people, and that is all I care about. It is frustrating to answer a question with a long drawn out answer, and the person who asks the question doesn't use the information you spend 30 minutes typing. Looking at all the questions you have asked, it is easy to see you need to hire a mechanic to get it running right.
Glad to help out, Good Luck!!!

Answer 2

The idle mixture screw (there's two) is located to the left and right of center while you face the Q jet itself. If necessary pop the limiter caps off and bring your idle speed up to 650 RPM. Install a vacuum gage to the carb. below the throttle plate. Adjust one screw at a time in and out to get the most vacuum and RPM. Repeat on the opposite mixture screw. May I suggest you consider a large paper book available on amazon.com. It's: Rochester Carburetors By Doug Roe HP Books Tucson AZ.. I think Doug's wife is selling these books because Doug is deceased. This is by far the most instructional Rochester carb. book I've ever used. It has a dynamite high performance section with GM part numbers of jets, metering rods, accelerator pumps, floats, inlet needles and seats and other parts. Everything is spelled out thoroughly. The author, Doug Roe graduated from HS. with my mom and dad. He started out by working for the Eclipse factory in Elmira Heights, NY engineering the old Stromburg carburetors in the 40's and 50's. He later worked directly with Rochester, Pontiac, Chevrolet and for himself in Arizona. I've done a lot of Quadrajets in my day following these instructions with excellent results. I still have trays of metering rods, rod hangers, jets, power valves, floats and gaskets. They'll run as well as an expensive Holley or better. The grandaddy Qjets off Cadillacs, big Pontiacs and Buicks would flow 850 cfm's.

Answer 3

I agree with the 1st post. qjets are easy to rebuild as is the holley double pumper carbs. it may be time to rebuild your carb too. sometimes you can adjust all you want and it still donr run right. . I did that on my 69 buick. adjusted till my hands were numb. rebuil ti and it ran like a top like it just came from factory no hard starts , run ons , hesitations, rough idle all gone. funny how 30 bucks can make a car run soo much better. Not like todays EFI