A friend of mine called me the other day with a problem that is out of my realm of knowledge, so I though asking you Hambers might get him a solution. The car in question is a 1970 Buick Lasabre with a Buick 350, auto trans, and Quadrajet carb. According to him all 4 barrels are only opening when the car is in Park. He said only two open when it's in gear. This struck me as odd because I would think the secondaries should never open unless it's under load, is that correct? He also told me that he had the carb rebuilt a few years ago by a very reputable old timer and has never had any problems with it, but the guy died so he can't ask him for advise. He also replaced all of his vacuum lines when he first noticed the problem, but it didn't help him. Any help would be greatly appreciated. Sent from my iPad using The H.A.M.B. mobile app
Need a little more info, that really doesn’t make a lot of sense. If all four barrels were open in park, your engine would be at 5000+ rpm. He is probably referring to the air valve/ flapper or something like that. Bones
Yes..More info We're getting a 2nd hand related attempt at diagnosis here. I' m not clear at all on the symptoms, so far.
Something to look at is the small secondary block off lever that is activated by the choke. It keeps the secondary throttle shaft closed if the choke is on. Passenger side, mid carburetor, at the base.
Let's go with what we know, for now. No, that's not correct. The secondary butterflys will always open when the throttle is depressed about midway or more. (unless the choke interlock is still on.) You may be talking about the secondary flapper, which will never open unless the engine is running. It might open quicker in neutral or park, rather than it would in gear. That depends on several factors , which should only be discussed at bit later in this exercise.
Check to see if the vacuum diafram which holds the secondary flapper closed at idle when manifold vacuum is high is working.You should not be able to open that flap over the secondaries at idle
Sorry about the second hand info. I'm just going to have to see it for myself, but thanks for your input given such little info. I'm going to tell him to look into the item you guys are mentioning. Thanks guys. Sent from my iPad using The H.A.M.B. mobile app
It's been many years since I raced QJs in the late 60's. so my recollection may be faulty and subject to correction. It sounds like your friend may be a little confused at what he's looking at. I believe the secondary throttle butterflies are mechanical and are going to open at some point in the throttle cable movement. The air "flapper" deal above the butterflies is opened by air flow and as I recall, is adjustable so it can be made to open with a puff or adjusted for more resistance. So the questions are...... Is he checking with his head under the hood, ignition off? Or with the ignition on, blipping the throttle expecting to see the "flapper" open? Is the engine warmed up so the choke is not the issue? Apparently, the car runs so what exactly is the problem? Has it less power than normal on the road? Maybe you better add checking the kick-down on the trans to the list. All my betters out there...... If I'm wrong on how the QJ carb functions, by all means, correct me. I'm far from an expert.
Lots of good questions here, Shifty Not sure you can call the secondaries mechanical . They use a wound spring to move the secondary link. This way, you can still open the throttle all the way with only two barrels , while the choke is still on. Carry on, bud
They guys have a pretty good handle on it and The Shift Wizzard gave a real good explanation. The secondary air valve isn't going to open until the engine demands enough air flow to open it. That with the choke linkage blocking it until the choke is open and that air valve diaphragm working right. Years ago I lot track of the number of guys who though the 4 barrels weren't opening because they were reaching in and working the throttle by hand with the engine off and the secondary air valve didn't pop open. I even picked up a couple of pretty decent Quadrajets real cheap after guys swapped to Holley or an old AFB.
I suppose. I guess you could say you have another mechanical part not allowing them to open in certain circumstances.
Thanks for that addendum. That makes perfect sense. I had fun working on 'em 50 years ago but don't ask me to do it now. I'd fudge something up. Used to be I'd make 'em fast but now I'd only make 'em half'fast.
The Jalopy Journal
