71 Chevelle SS 454 LS-5. When I'm over 3000 RPM my Q-jet secondaries don't open.....Why? I've tried 2 new carbs and they both exhibited the same problem. Is there too much vacuum and the butterfly spring can't overcome it?

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I could be wrong on this ,but it sounds like you Do not have enough Vacuum to open the secondaries.Check your source with a vacuum gauge,and see how it reacts.
You could also have a binding or the secondaries are hitting maybe the gasket under the carb.You can open your secondaries manually to check that they open easily

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Ricks 64 SS Convertible (http://www.geocities.com/pinball4570_win/classic_white.html)

desert heat,

There are a couple possibilities here, is it the throttle butterflies or the airvalve on top that doesn't open?

There is a lockout on the secondaries, won't let the throttle open unless the choke is completely off.

Generally, if the engine is warmed up to temp, with the engine off, open the air valve with your fingers and open the throttle to WOT with the other hand. You should see the big round butterflies open to straight up or almost straight up. Try that and post your results, we'll figure it out from there.

Tom

I tinkered with the Q-jet today. The choke is definitely wide open and the linkage that mechanically locks-out the lower secondary's (passengers side) is not the problem.

The secondary top butterflies opens very easily when I touch it with my finger so I don't think it's the top secondary's.

I checked the gasket; there is no binding. Remember, under 3000 RPM, the secondary's work great.

I'm thinking that if I can wrap the secondary spring 1 wrap tighter (if possible) on the lower secondary shaft on the drivers side, this would apply more opening force to the lower secondary's, thus overcoming the intake manifold vacuum.

Thought????



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Desert Heat,

I've been a Q-Jet builder for too many years to think about, I've never seen or heard of this before. Can you say what it is that's making you think the secondary throttle is not opening? I'm thinking that you're feeling a slight a hesitation when you stomp it below 3,000 and nothing but pure throttle response above 3000, leading to a conclusion that the secs are not opening above 3000. Or you're feeling an auto trans kickdown below 3000 and it's not kicking down above 3000 or something like that.

Do you have access to a chassis dyno where the behavior could be observed with the hood up?

What is it that makes you think it's not opening?

Tom

2000 RPM...stomp on it...deep growl from the secondary's, cowl induction door opens (low intake vacuum), car takes off like a bat-out-of-hell.

2500 RPM....same as above.

3000 RPM...stomp on it..."no" deep growl from secondary's, cowl induction door "doesn't open, car accelerates slowly.

Also, when I'm getting on it and shift fast, the secondary's again don't open when I hit the next gear. Again over 3000 RPM.

I'm trying to characterize the problem and the common thread is "no secondary's over 3000".

Help!!!!

Where's the choke lock out on this Q - on the air valve or on the end of the secondary throttle shaft?

Hmm, does not make sense to me either. Opening of the secondary throttle blades is utterly mechanical. As long as the linkage is operating correctly, the choke lock-out is correctly adjusted (if on the secondary shaft), and the blades are not hanging up on something, there is no physical reason the blades would not open. Assuming that you can operate the linkage and actually SEE the blades open we'll assume that's not the problem.

The secondary air valve should open if 1) the secondary throttle blades are open, 2) air flow through the primaries is constricted enough that there's a vacuum created within the secondary venturies - thus pulling the air valve open, 3) the choke lock-out - if installed on the air valve, is not engaged, 4) the air valve dash-pot - if so equipped, is not hanging up. Obviously, too low a spring pressure won't prevent the valve from opening. Too high a spring pressure "could" but, given the symptoms you've described, I find this unlikely.

Yeah, sounds to me that the choke lock-out might be the culprit.

Do let us know what you find.....

Dan

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Awww, fer cyrin out loud, there's that IMPALA guy again.

http://photos.yahoo.com/bc/ss3964spd?d&.flabel=fld1&.src=ph

What is your vacuum at 2000, 2500, 3000 ????
And what happens to it(vacuum) when you punch the throttle ?????

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RicksRag
Stephen City, Va
TC # 560
ACES # 3702

That sounds like the secondary lockout from the choke. Wire that lockout lever down so it does not move then see what happens. Also just for giggles try pulling the vaccum line off the choke pull off and plug the vaccum source. That will tell you if your secondaries are working you should get a great big hesitation, then it will take off like gang busters. Maybe this will narrow your problem down a little.

Yes double check the lock out. Maybe you have two and for some unknown reason the one below is locking in at 3000, and why that RPM is magical we'll never know. Disable both. Test.

If problem still occurs then I suspect the vacuum can that your secondary airflap is linked to is either out of adjustment or faulty. Make sure that the rod that connect the secondary air flap to the vaccum can has pleanty of slop in it. It should allow the secondaries to open a bit when full vacuum is applied. Easy test. Start the car and see if there is a gap between the rod and the slot in the air flap. There should be. You should be able to tip the air flap in. If its tight, then bend that rod longer and give it some slack.

After that I'm completely stumped. You might have to punt and HIRE Mr. Mobley to track this one down.

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Gene
427TRI@chevelles.com
67 SS 427 (http://www.chevelles.com/feature/october2000.html)

[This message has been edited by 427L88 (edited 11-06-2000).]

Try removing the rod from the air valve dash pot.Then see what happens.

Guys,

I tried most of the suggestions you all gave to no avail. I eliminated the choke and the mechanical choke lock-out as the problem. I eliminated the air valve dash pot as the problem. I eliminated the secondary's hanging on the gasket as being the problem.

So......I studied the secondary shaft springs on the drivers side.

I opened the primary's all the way and the secondary's opened correctly (engine off). Then I manually held the secondary shaft, then opened the primary's all the way....I could easily hold the secondary's closed when the primaries are WOT, thus simulating a high vacuum that doesn't let the secondary's open.

I wanted to simulate my theory. I placed a piece of rubber on the outermost secondary shaft spring (there are 2) simulating an additional 90 degrees of spring pressure. IT WORKED!!!!

Now at 3000+ RPM my secondary's open as they should and my SS goes like gang-busters!

Now....does anybody know what the spring is called or where I can get a new one? (Secondary shaft drivers side outermost spring) I suspect the spring is tired.

Thoughts??

Desert Heat

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[This message has been edited by Desert Heat (edited 11-06-2000).]

[This message has been edited by Desert Heat (edited 11-06-2000).]

[This message has been edited by Desert Heat (edited 11-06-2000).]

[This message has been edited by Desert Heat (edited 11-08-2000).]

[This message has been edited by Desert Heat (edited 11-08-2000).]

Thoughts?

Is this the spring on the end of the throttle shaft? Maybe it's come loose and spun 360 degrees and now does not push as hard as it should. Can you wind the spring one turn tighter and reconnect it?

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NCOA member #220
ACES member #1670
Rich's 1965 Malibu SS Restoration Project Progress Page (http://www.geocities.com/motorcity/flats/8627/)
1:18 scale diecast car Detailing by Scooter (http://www.amhost.com/scooter/)

Problem solved!!!!

I took off the drivers side, outside-most secondary spring and bent it so to put "more" spring into the spring. Guess what.......it worked!!! I guess the spring was tired as I suspected. Better yet, I've been chasing this problem for about 10 years now. Best of all...it didn't cost anything!!

Thanks guys for the help!

Desert Heat

Damn, the better part of a decade on 1 carb... and I thought I had troubles. http://www.chevelles.com/forum/biggrin.gif

Good job on the hunt. Now get out there and do it to it.

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Francis Taracido Gold# 201
sniper0666@aol.com
History shows again and again how nature points out the folly of man.
Oh No! You Know She's Got To Go!
Go Go Quadzilla! <oo=+=oo>
http://members.aol.com/sniper0666/page/intro.html

I would have taken a ball peen hammer to it
after 5 yrs.