Hi All, I think I have some issues with my choke. I don't think it is working correctly. When I start my car the choke kicks in and the engine picks up RPM"s and maybe too many. But it takes forever for it to kickdown to regular idle. I wondering how long the choke should be "on" and what would cause it to stay choked soo long. I didnt think it was the rods since it does go down eventually. Thanks Gary
Gary, Is your secondary choke pulloff working? It's the one on the rear. Most don't realize it has the function of pulling off the fast idle once the engine is started. There are lots of adjustments to the linkages of QuadraJets that many guys don't understand. Howabout posting a picture of the passenger side of the carb so we can see if all of the linkages are intact? It should look like this
The easiest way to understand the operation of the choke is to understand the purposes of each part of it. The choke is intended to do one thing. It is to restrict the incoming air flow, to make the mixture richer, compensating for the loss of fuel due to condensation. This condensation typically is on the inside of the cold intake manifold, and the heads. Also, as the incoming air is colder it adds fuel to compensate for its increase in density. The choke does two things when it closes. The first is to close the choke blade, maximizing the enrichment for a quick start. At this point, the fast idle cam is also raised, raising the idle. This assists in the fuel vaporization, and overcomes the internal friction in the engine, due to cold oil, and temperature tightened parts. The choke, at this point, should be completely closed, especially if the engine has not been run for six hours. When you push on the blade, there should be a noticable resistance attempting to close it. Once the engine starts, the choke pull-off will open the choke slightly, allowing the engine to breathe. This typically does two things. It leans the mixture to prevent flooding, and it still enriches the mixture sufficiently to prevent hesitations and stalling during warm-up. Adjustments here allow the engine to run properly as the choke coil warms, pulling the choke completely off. If the pull-off is set too rich, or is not pulling the choke completely open, the engine will run lazily, slow to rev, sluggishly, and may either emit black smoke, or cold flood. If, on the other hand, the choke pull-off is set too lean, the engine will hesitate on acceleration, or may stall. Usually, the place to start with adjustments here is to measure the distance the blade opens with the pull-off fully seated, between the rear of the choke housing and the blade. You should see about 1/8". As the choke coil heats up, the blade starts to unload, allowing the engine to receive more and more air, and allowing the fast idle to gradually drop to normal idle. Once the engine has run about two minutes, problems with the adjustments, including hesitations, sluggish performance are more due to the speed of the unloading, not the pull-off adjustment. With respect to the fast idle, too frequently, incorrect choke adjustments require unnecessarily high cold idle speeds. As the choke starts to operate properly, as noted by its performance cold, it is easy to start reducing the cold idle speed. The actual speeds are set points, not something etched in stone, and the better the engine performs cold, the less idle speed are necessary to keep it running.
Gary, Duh, I've looked at this thread several times and more on the other thread about your car(I want another 350 car) and I should have realized it was a 70 carb which is what your picture is.ou: I had to go back to see the 7040244 as opposed to the 7042244 that I thought I was seeing. The carb in my pictures is a 71(7041544) and it has a different choke system but other than that they still are both Buick specific carbs. Does the primary pulloff on yours funtion correctly? Howabout do all the linkages move freely when the choke rod is disconnected? There are a whole bunch of adjustments to be made even on your single pot choke and they have to be done in a specific order for them to work correctly. Do you have access to a 70 factory manual or even the instruction sheet that comes with all rebuild kits? As with most choke probs it will be a simple matter of baselining the correct setup then adjusting from there but most of the time once everything is back to spec, you don't have to mess with them anymore.
Hi Dave, Yes I have a manual and will check it out. Going to buy a vacuum pump today since mine is MIA to check that pulloff. Will let you know. THanks
You don't need a vacuum pump to check the pull off. All you need to do is remove the vacuum line, push the link in by hand, then put your finger over the vacuum hole, and release the link. It will either hold the link in, or not.
Looks like you have a 4MV Q-Jet, just like mine: ..though mine has the idle-vent, but we both have the single choke pull-off on the passenger side. The choke coil rod needs to be adjusted, first, to ensure the choke is being closed when the engine is cold. This measurement is done by holding the rod connected to the coil completely up (to its highest point), and fitting it into the STD slot with the choke held shut by bending the rod attached to the choke coil. Yours looks to be in the correct location. The rod connected to the vacuum break diaphragm will pull forward and open the choke slightly once the engine has started and manifold vacuum is present. You need to adjust the choke tang here: ...and bend it so that when the rod contacts the tang, it pushes your choke open slightly. The tang on your carb looks like the 90-degree elbow in the vacuum-break rod is never going to hit it. I'd bend the tang back a tad. I'm not sure what the correct setting is for your carb, I'm thinking around 3/32"....I need to adjust mine as well. My starts are sometimes sporadic: when cold it fires instantly - then dies out. I think my choke is not opening quickly or far enough once the engine catches.
