I have a Rochester quadrajet. I traced the numbers back and it was produced in 1970 and was in a Pontiac. The problem is that it doesn't open up. It just stays closed unless I put something in it to hold it open. Any advice? Thank you

 

What does not open? The choke plate, secondary air flap or ??? Give us some specifics or better yet a picture of what will not open and we will figure it out!

 

It's the secondary air flap that's stuck. The piece that moves it up and down doesn't move at all and I think it's not hooked into whatever it has to hook into.

 

Pictures would help here.

 

Check to make sure that the choke lockout is free and working .it is on the throttle shaft under the choke.when the choke is fully open it should move out of way. Also check how fast is the choke pull off diaphragm. When you depress it and let it go it should return in about 3 seconds if it is more it needs to be replaced but that problem is a rare occurrence. Can you flick the air flaps with your finger dose it open easy and smooth.if it hard or binding clean the shafts with carb clean while moving it open and close.let it dry and do the same with a little w-d like lubercant.this is the most likely I worked on a few cars that the owner were putters that they never got on the gas hard to open the secondary ever. Then dirt and grime wound make it stuck.

 

Are you manually checking like Grampy suggests or trying to get them to open by revving the engine in neutral? The latter won't work since the air flaps on vac secondaries only open under load.

 

It's the secondary air flap that's stuck. The piece that moves it up and down doesn't move at all and I think it's not hooked into whatever it has to hook into.
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The upper secondary air valve is operated by the air flowing over it. It is supposed to be shut normally, with engine off or with little airflow into the engine- idling, light acceleration. May I suggest you study up on the operation of the QJet? Start with the chassis service manual. Grab a parts carb and become familiar with each and every part. What it is supposed to do, how it does that, etc. It seems intimidating at first, but there are not that many items, really. Other folks have done it, so can you.

 

When you say, "secondary air flap", I assume you mean the secondary air valves that are on top, right. They are opened by vacuum when the (lower) secondary throttle valves are opened when you floor it. Nothing mechanical opens them, but as mentioned, there is a lockout on the right (passenger) side that blocks the valves from opening until warmed up. Pictures, pictures, pictures would sure help.

 

Technically, it isn't "vacuum" that opens the secondary air valves, it's mass flow over the blades, but as noted, they open in response to load. This question comes up about once a week and is a perfect example of why it pays to fully understand how your particular carb works. You WILL NOT see those air valve open more than a crack if you are revving the engine in PARK, simply because you don't have enough load to generate sufficient mass airflow. And as noted, the lockout tab is connected to the choke linkage, so you can't even open them manually until the choke warms up.

 

Here you go

 

Okay, I'm confused. I see a white cap of some kind stuck in the PRIMARY side. Are you referring to the choke rod that is pretty close to the middle of the picture, as the rod that goes down and is doing nothing? That connects to a cam down in the carb. That cam is on the shaft of the choke assembly, and it opens as the engine warms up, and pushes the rod up and opens the primary air valve. The spring in the choke closes the primary air valve, which is held open in your picture with the white cap, by pulling the rod down when the engine is cold and closing the primary air valve.


That has nothing to do with the secondaries. The secondaries are the larger valves on the left. If I am not understanding you right and that is not what your are asking about, which rod are you referring to?

 

Yeah..the air valve doesn't open or close...that rod wasn't hooked to the cam in the carb. Is there anyway I can take that out and hook it back up from underneath? or if it's even possible?

 

First, look down the hole of the rod. Is the oval shaped cam on the shaft of the choke? You can push the choke linkage so the cam is in it's highest upward point, and then drop the rod down and get it in the hole in the cam. It is easier if the carb is off the car, otherwise you probably have to lay over the fenders and hood to see the cam, with a light. It is a pain and may take a number of tries, but you can do it. Also, you need to remove the upper screw that attaches the rod at the top. The bottom of the rod bends at a 90 degree, and will point toward the outside of the carb to engage the cam. Then you have to carefully push it back on the upper and re-install the screw. When you get the upper against the place it attaches, you will need to open or close the primary valve so it lines up the flat spots on the attachment area and it will engage the top and you can attach the screw.

 

As others said before you posted this, it is NOT an "air valve." It's the choke butterfly.

And as Brown says above, unscrew the tab that the choke rod attaches to, mark the position of the black plastic choke spring cap, loosen the three screws that retain the choke spring cap, grasp the choke rod with a pair of needlenose pliers, rotate the choke spring cap to get the right angle on the cam or tab at the bottom of the hole, and guide the end of the choke rod into the hole, then reconnect everything.

- Eric

 

One of the things that can make these discussions confusing, especially without good pictures, is many of us call the same parts by different names. I called it a primary valve, Eric called it a choke butterfly. Actually, according to the Olds Parts Manual, 1970-72 Q-jet it is called a choke valve. To make things even more confusing, for the 1973-74 Q-jet, the same part is just called a valve.

 

Very true.

"Choke butterfly" is the commonly understood term for the part that fulfills that function in all carburetors, though, regardless of what Rochester chose to call it, which, as you note, has changed over the years.

It is a very reasonable discussion to have. In my case, I try to use the most universally understood term for any given item, unless the item is extremely specific, such as in a previous discussion of dashboard "flood lights," in which case I will use the oddball term that GM chose. For instance, you could call the item behind it the "secondary flapper" or "rear air valve," but it is a unique QuadraJet part, so I call it what Rochester called it, a "secondary air valve."

- Eric

 

Let's revisit post #7

It's time to learn what all those things do and how they are supposed to be hooked up.

Sometimes you can unscrew that choke rod link at the top and finagle the bottom into its hole way down in there and then re-attach the top.

Secondary air valve lockout appears to be missing. With that much wrong just at 1st glance, chances are much, much more is wrong inside and everywhere else.

 

I am NOT an expert on this, but somewhere in my mind, I think I recall that Poncho carbs may have the lockout as part of the linkage on the side of the carb, involved with the vacuum delay diaphragm.

- Eric

 

It looks to me like the lockout is missing. It attached to the roll pin beside the choke rod. When the choke valve (butterfly) is closed or not fully open, the lockout on the roll pin extends over on top of the front edge of the secondary air valve and prevents it from opening. As soon as the choke is fully off, the lever extends all the way up and it pivots the lockout so the secondary valve can open. I always remove mine. If they malfunction, you have no secondaries. I don't get on mine until it is warmed up, so it serves no purpose for me.

 

The 4M carb he has should have a lockout up on the air horn - its not there

the carb has been converted to the M4M (75+) electric choke arrangement, and that qjet had the lockout mounted down low on the rearmost choke housing mounting post on the main carb body. This also appears to be missing

Neither of these would jam up the choke flap.

Is it possible that there is a binding occuring between the M4M fast idle cam - and the 4M choke cam follower mounted on the throttle shaft? I mention this because unless I am mistaken, the throttle shafts 4M to M4M are slightly different lengths and would cause a misalignment (choke cam to cam follower) unless corrected.

Time to go through that choke setup. Pull it all off and make sure youve got all the right matching pieces, then reassemble.

 

The problem as I understand it, is the choke rod is not connected to the choke shaft and the choke valve is free, and doesn't stay open. Has it ben determined that the choke rod lever is attached on the intermediate choke rod (down below)?

 

Did this carb come from a running engine? After the links and flaps are sorted out, but before the engine is run, be sure to slowly depress the accelerator pedal to the floor and release it to be sure that the linkages will not hang up and hold the throttle open.

 

Thank You all...I took my carb off and got all the linkages and stuff hooked back up.