I know nothing about Carbs:bla: I can't get the secondaries to open on my GS... Should'nt they open if I goose the throtle (at the carb) when the car is in drive(edit, I meant Neutral)? I just replaced the my original carb with a new one and even my original carb would not open the secondaries. I don't hear the massive air sucking sound when I hammer it when driving so I do not think they are opening when the car is moving either. From a dead stop I can punch it and break the rear tires loose though:TU: What should I check? Stock '68 GS 4bbl Rochester Carb.
Secondary flap will not open for you while you are working on it. They open only under a strong load when air flow is needed.
Not a good idea to put the car in "drive" then lean over it and goose the engine....:spank: The secondaries are mechanically prevented from opening until the carb senses a large increase in air flow. Putting the car in "drive" will actually make it even harder to make them open..... Have you checked your throttle linkage? With the car turned OFF, have someone mash the throttle to the floor. Check the carb to make sure that the primaries are opening all the way- 90 degrees. If the primaries don't open all the way, then the secondaries won't open all the way either.... Also, if you put a larger or non-stock carb on your car, the secondaries can physically hit the intake manifold- that will prevent them from opening, and even jam them partially open all the time. This happened to me, and I had to install a short carb spacer so that the secondaries did not hit the manifold. Manually manipulate the air flapper above the secondaries (hold it wide open), and make sure that the secondaries are opening with full throttle.
I'm not sure if your 68 has it, but the 70 choke linkage has a little arm that will keep the secondary spring loaded air valve locked closed until the choke is fully warmed up (assuming it's adjusted correctly. It's also possible that someone monkeyed with it during the gas crunches in history and would keep it from opening.
1) Ive seen some 68s that have a little arm thing, its located on the air horn, passenger side, on the back side of the primary bores. When the choke is closed all the way (cold start) there is contact that makes this arm stop the air flaps from opening. This arm's action is adjusted via the choke linkage. 2) Be sure the air flaps will open by hand ie they arent frozen shut or something. Feel for their tension. There is a spring that can be adjusted that puts tension on them. If thats wound far too tight, it -could- hold off opening. Adjustment is done on the passenger side, there is an allen head screw on the underside of the air horn holding the spring shaft, right by the air valve's shaft. Loosen the screw and it should release the spring shaft tension. Use a jewelers screwdriver to adjust it to specs, or about 3/4 turn tighter than air flaps closed. 3) The other thing that impedes the movement of the air flap is the primary choke pulloff, located on the front passenger side of the carb, attached to the choke bracket. This is hooked via a link to the air flap, and connected to manifold vacuum at the passenger front of the carb. The canister should release in about 1.5-3 seconds from fully depressed to fully open. It should be fully drawn in at idle, and should release when vacuum drops (WOT etc). If that pulloff is releasing slowly, it is possible that it will give the appearance that the secondaries wont open, when the motor is revvved quickly in neutral, even if it operates properly when driving. Adjustment of the canister is done by changing the size of the orifice on the vacuum side of the unit. Too fast a release = bog. Too slow = impeded performance. 4) My final thought is to check the air flap cam in between the two air flaps. sometimes these break on older carbs. Maybe its jamming the air valve shaft? Just a shot in the dark.
Try this, pull the throttle linkage to the full open position and the mains will free a small cam linkage Hold the throttle rod in the full open position and press down gently on the secondarys. They should fall open if they are not jammed by something. Secondarys do not have any linkage that opens them, they rely on engine vacuum to do that, as said in the other posts. Sometimes air filter housings will impede operation of the secondarys also, and you said you replaced the carb, so check that out as well.
Why noto No: :laugh: :laugh: It was in neutral:laugh: Thanks guys, I have a few things to go back and look at after seeing your replys :TU:
So, if my 350 makes the secondary butterflys open real quick then shut when I goose the throttle while the car is idling in park...is this a good, normal, thing or a sign of something lacking?
Mike, The flaps up top are called secondary air valves. The air valves effectively size the carburetor capacity to engine demand. They will only open when the engine demands the additional air flow. The secondary throttle valves will open via your right foot. You should verify that they are opening all the way when your foot is on the floor. With the engine off, have someone mat the gas pedal while you tip in the air valves and verify that the secondary throttle blades are open. I'm sure you have heard about the dreaded Q-jet bog. Most of the time, it is due to the air valves flopping in too quickly. There are two things that dampen the air valve movement. One is adjustable spring tension at the air valve shaft. With the engine off, if you tip in the air valves with your finger, they will close when you remove your finger. That is the spring tension at the shaft. The front choke pull off also functions to slow down the air valve. With the engine running, high vacuum pulls in the choke pull off lever which is also linked to the air valves. The choke pull off holds the air valves closed under high vacuum. With the engine running at idle, you should not be able to push the air valves open because they should be held closed by the choke pull off. When you are driving the car and you floor it, the engine is under high load. The vacuum drops quickly, the choke pull off relaxes and the air valves tip in as the engine demands more and more air. You can't make that happen by reving the engine from idle. You can't make the vacuum drop fast enough to let the choke pull off relax the link holding the air valves closed. If you pin the throttle really fast and let it go, you may see the air valves budge a bit, but they won't open all the way like you expect. If they did, something is wrong, and you would be experiencing the "Bog" Hope that explains it.
Mine do open wide open from idle in park. So my problem is the resistance to them opening is worn out? When i push them open by hand with the engine not running they do spring back.
I think I am going to learn alot about carbs :laugh: The secondaries do open "slightly"or just start to move when in park and I jab the throttle so it may not be a problem. Today I noticed other problems. 1.) hard cold start and would not go to fast idle, had to keep my foot on the gas to keep it from stalling. 2.) once warmed up it will die or almost die if I jab the throttle either in park or in drive, I did not notice this problem yesterday. ou:
I believe you are experiencing the throes of a neglected carb and the crap we lovingly call fuel. It is very easy to throw a carb "kit" at a carb and say that it was rebuilt. Rebuilding a carb simply means putting the carb back in the factory condition, using parts compatible with the chemicals presently used in our gasoline. 99.9% of the time, the kits come from overseas, and contain the materials used in the kits from 50 years ago. These include seals, gaskets and moving parts not compatible with our fuels, and frequently installed by individuals who have never seen a carb before. Bear in mind that the Qjet essentially disappeared in the 1990's, and, for the most part carb theory is not taught in schools anymore. If it is taught, there is a passing comment regarding the beauty and simplicity of the Holley carb, as if no other existed, meaning that most in the field appear as a deer in the headlights when they see a real Qjet. I offer two suggestions. One is to address either Cliff Ruggles, or John Osborne with the carb you have. I know more about Cliff Ruggles, having successfully used his book. In his book, he successfully describes the carb's needs, and has, in stock, the parts you will need to successfully FIX your problems. My experience at GM as a service tech, in the '70's, '80's, and '90's, is essentially reflected in Cliff's book, telling me that he has the experience, know-how, and desire to assist you. Once the parts have been successfully installed, you can tune successfully, and have the satisfaction of a job well done. Something to consider here is YOUR value in the future of this hobby. My 50 years experience in this industry has proven invaluable to many seeking assistance with older vehicles, and in modified ones. Unless someone grabs the bull by the horns, the experience dies here. From my experience, it is very difficult to find those interested in embracing the past, and those interested in learning from those who were there. It is not difficult to embrace this hobby, and you might enjoy its "moments." My suggestion? Purchase a kit from Cliff, purchase the book by Cliff, and try it yourself.
Hmm, I'm one of those, that is what I am trying to do, should I start my own thread to ask my questions?
"I just replaced the my original carb with a new one and even my original carb would not open the secondaries." "New" one from what source? They haven't made "new" Quadrajets since Edelbrock discontinued them a few years ago......Cliff
Worn? I think you need to go back and read my post again. Check the spring tension with the engine off, and simply look at the front choke pull off with the engine running. Vacuum is either pulling the link in, or it isn't. And there should be a metal linkage from the choke pull off to the air valves.
Hard cold start? I would look at the choke. Is it closing when the engine is cold, and you pump the gas once? There is a stepped fast idle cam that rotates with the choke blade. That is what provides your fast idle speed. You need to inspect the linkage and choke. Again, check the spring tension of the air valve shaft with the engine off. Then start it and observe the front vacuum operated choke pull off. See if it is working and if the metal link to the air valves is in place. You should not be able to open the air valves with your finger with the engine running.
Cliff, It is a '68 GS400, auto trans carb that had been rebuilt (not by me). I need to rule out that I did not do anything wrong when I installed it. I don't know what I am doing (trying to learn) so I have not tried to tune it at all... My hope what was that I could just install and go, I should know its never that easy especially when you don't know what you are doing ou: :laugh: I will look at the choke area to see what is going on there.
Yes, when it is running I cannot push teh flaps open by hand, the choke pulloff is pulling on them keeping them shut. The adjustable spring also makes them snap shut when I push them open by hand when it is not running. Does this mean I need to tighten the spring tension more as my only recourse, would you say? Or is there another way the choke pulloff could be failing maybe?
