The quadrajet on my W30 75 Hurst Olds just about has be at my wits end. When I bought the car back in October it surged like crazy at idle. I put a kit in the car and in spite of my screwups which I corrected it was better but would not consistently idle at the same RPM's and was hard to start. I found the correct number carb on ebay that was a factory rebuilt that had been on the shelf a while. I put an electric choke on it and installed it last Saturday. It cranks perfectly and runs smooth with one exception. When you put it on the floor it stumbles. I remembered having the same problem on a 79 Cadillac many years ago. I remember tightening the tension on the spring on the air dampers over the secondary venturi. I probably have these about as tight as I can get them. I have actually over tightened them a couple times and had to take the carb off and put the spring back on with some small hemistats. Am I missing something here? Anybody got any ideas?
Thanks Guys

 

Have you checked the secondary rods and hanger to see which ones your carb has?

Another thing that comes to mind is one time in the 80s after rebuilding the carb, one of the air bleed tubes fell out of the air horn. That caused a nasty bog at WOT.

 

Is the choke pull off and linkage installed?

 

Glenn, if you give it the beans from a roll and it bogs, it's not the secondaries. Booting it at 60, on the other hand, is the secondaries.

My Chevy had no power at 60, like surge, thud, surge, thud, surge, thud. No fuel to secondaries. Does yours get going after the bog if continued to be floored?

 

Car runs perfect until it is floored. I can floor it at 60 and it bogs. Let off just slightly and it is fine. The choke linkage and pulloffs are fine and I just installed an electric choke which works perfectly. I will check the air bleed tubes when it warms up. Car runs great up to about 90% throttle. I have a love hate relationship with quadrajets.

 

Cliff Ruggles has high performance choke pull off, that may help. You could notch the blades if the secondary discharge nozzles are above the secondary air valve, which most are. Good luck.

 

If you are going to repair or tune Q-Jets I highly recommend reading these before you open the hood.

 

Glenn - What is the model number of your Quadrajet? Let's see if it's the correct OEM model for your engine.

 

The csm has a very good section on setting the q jet up to the factory specs including the secondary spring wrap. I went thru my rockauto remanned qjet and while most stuff was in the ball park everything needed a little attention.

in the end i bolted on the carb after adjusting everything, anywhere from idle to hiway speeds i floor it and it just goes no bog no hesitation

 

Thanks guys. I am probably going to order Clif Ruggles book. Norm it is the correct carb (I have two now) with number 7045184.

 

Doing every adjustment precisely and in the prescribed order usually ends in a good running Qjet. Fine tuning after getting all the basics on spec can reap additional performance.

You'll enjoy and learn from the book. Good luck!

 

I have rebuilt several quadrajets over the years but his one is just kicking my butt. I ordered Cliff Ruggles book this morning. It is not cheap but less than a new carb and cheaper than having somebody else do it. I may do take the one I took off the car that is on the bench and go through it.

 

Glenn - OK, Correct carb. I have Cliff’s book and a couple others, I’ve rebuilt a dozen Quad’s IMO super simple. Tough to diagnose when it appears only at WOP I believe you said (I’m on my phone). When I get back in my PC I’ll review a couple things. Too hard on a phone.

 

Thanks Norm. When they are right they are great, when they are off they are a PIA. Out of two carbs I should be able to get one to work.

 

Glenn - Back inside.

The basics: It runs smoothly at idle - great. Stumbles on demand going WOT. Most likely adjustment on the secondaries. If nothing appears to be an issue with linkage it's most likely the secondaries spring tension is far too tight. Wrong spring whatever. Once you have the appropriate spring, you need to establish the zero balance of the spring to the secondaries so the dampener effectively operates but also the the secondary throttle blades are being pulled too tightly. This is accomplished via the two screws: (1) One screw is a straight-tipped flat-head screw at the end of the choke pull-off (towards the rear of the carburetor). It's that screw which actually adjusts the tension - you shouldn't have to overtighten. But, if you do over-tighten don't forget you need to adjust the (2) Allen screw underneath. That Allen screw sets the spring tension to the zero position so the secondaries are for the lack of a better word, operating in "unison". If you tighten the flat-blade screw without readjusting the Allen screw underneath you'll have an issue with bogging going into WOT as you'll have far too much spring tension. This guy has it right in the video. BTW, I've seen guys remove that metal blade when they've given up assuming that metal blade (bar) MUST be the culprit. LMAO Check it out.

 

Glenn - I think in the above I may have stated it backwards (I'm working outdoors and have a couple things going - sorry). At any rate, my hunch are the two adjustment screws. The Allen screw adjusts the tension, the flat blade locks it in. Unlock the flat blade lockdown screw (which hold the correct tension), adjust the Allen screw to the correct tension, then tighten the lock-down (flat-blade) again until you have the proper tension. Obviously, without stating such, the choke/secondary dampener linkage must move freely with no restrictions (which I suspect is fine on your carburetor).

I'm installing a new (restored) OEM clock in my '71 CS & greasing the speedometer cable so this small break has allowed my back some time to rest - on the floor working on the instrument cluster seems harder than when I was 16 yrs. old.

 

Oh hell - I'm all over the place I guess. I think the Allen screw is the lock-down screw and the flat-blade screw is the adjustment screw.

 

Norm I am very familiar with the tension screws on the secondary air dampers. The are a pain. I have used a mirror to loosen the allen head set screw. I remember on the 70 Cadillac that I mentioned in the first post that I believe I had to tighten it to stop the bogging which seems the opposite of what you would normally thing. I am pretty sure the tension on the air dampers is the problem. I am going to wait until the Cliff Engles book arrives. All the choke linkage is in very good shape. Thanks for you help.

 

If it wasn't 23° here and sleeting I would probably go out and loosen the tension on the spring. It was 74 on Monday when I was fooling with this thing.

 

Glenn - OK. Yeah, getting the tension screws takes several runs. For WOT issues though, I've found the secondaries' tension to be the issue.

 

It's that very ever so slight delta between the rods being seated "firmly" or not being seated "firmly". If the tension on the secondary blades don't allow the blades to open/close with the correct tension, the rods will float above the seats and create the bog. Good luck, Glenn.

 

Yes, the Allen screw is the lock screw for the spring tension screw. In my experience, an adjustment as small as 1/8 turn of the screw made a huge difference in operation.

Another thing to check is the vacuum pull-off to ensure it is working correctly.

 

My experience has been that too much tension does not cause a bog, it just slows down the power transition. Tighten enough and you end up with 2bbl carb operation. Been there, done that.
Too little tension allows the air doors to open too fast, resulting in too much air flow, and a resulting lean bog.

 

^x2^ Exactly. Takes several runs down the road to dial them in. I think I generally started with like 1.5 turns CW.

 

2 things to check. 1.The choke pulloff controls secondary opening rate, disconnect vacuum line at idle & verify slow release. 2. Have someone sit in the car with ENGINE OFF and floor the gas. Look down the secondaries with flashlight and verify full throttle blade opening. I've heard of fuel slosh causing stumble but very rare. Maybe check float level & timing.

 

Since you are dealing with the air valve, would be worth looking at the plastic cam in the center that actually lifts the secondary rods when the air valve opens.
Many times they are wore out or plain a$$ broke.
could cause a lean bog.

 

Reading back to OP. If you over tightened spring to the point of losing it. Good chance you wrecked the spring and no amout of adjusting it will bring back the proper tension.
Cliff does offer a kit that has both the new spring and plastic secondary cam.

 

Yes, too much tension is not bad, just not optimal. Too little is bad due to bog.

This is the gentleman's approach. Holley, on the other hand, just gives you another accelerator pump back there, has no air valves, and just dumps a lot of fuel overboard when you bury it until the engine catches up.

 

Cam in the center is good and lifts the metering rods when the dampers open. Yes I did overtighten it a couple times and had to take the carb off and take a small pair of hemotats and get up in the cavity where the spring is and put it back on the pin that goes through the end of the shaft. Believe me guys, I know this thing better than I would like to.

 

I completely understand what you are saying.

 

Rereading this and I remember having a similar issue - back off slightly and the engine "catches up" - but it was so long ago (1980s maybe?) that I can't remember what the problem was.
Fuel pump failing?
Float level too low?
Maybe it will come to me later.

 

No doubt. I'm putting a spread sheet together with bets - $20/member to enter. I say it's the secondary throttle plate spring adjustment tension screws need to be finalized. Getting it right doesn't happen in the idle (everything is coming up roses) state. You have to drive the car several runs to get 'em right. Loosen both screws, close the secondaries. Turn the flat head screwdriver set screw until the secondaries are held closed modestly tight. Then, turn 1.5 turns CW. Take it for several runs repeat loosening or tightening the secondary throttle plate tension screws. IMO, if it works flawlessly at idle, but not during WOT, it's secondary adjustment. Let me know if you're interested in the spread sheet pool - I'll give you an address to send your money.

 

Yep, just toss fuel until the engine catches up.

 

I remember on the Cadillac I had it was the tension on the air dampers or whatever they are called. That was a long time ago and I don't remember how the heck I figured it out because their is no mention of that in the kit. I also remember putting more tension on the spring. Thing almost drove me crazy and now her I am at 75 still screwing with one of these damn things. I think sometimes we are just gluttons for punishment.

 

Correct.
I think the Secondary Air Valve spring adjustment is covered in the CSM.
I used to:
1. Insert a 3/32" allen wrench in the SHCS to release tension on the spring (and leave the wrench in, if possible).
2. Fully open (manually) the Secondary Air Valve.
3. Insert the straight blade screwdriver in the screw slot and turn CW.
4. Slowly turn the screw CW until the Secondary Air Valve closes.
5. Turn the screw CW 1/4 turn more.
6 Lock the tension adjusting screw by seating the lock screw (3/32" allen wrench)
7. Scribe a fine line next to the screw slot as a point of reference in the future.
If you experience bog, adjust a maximum of 1/4 turn more. If there is still bog, look elsewhere for the problem.

 

[=Fun71;1403018]Too little tension allows the air doors to open too fast, resulting in too much air flow, and a resulting lean bog.[/QUOTE]
You’re about 3/4 the way there as to why it really bogs. Care to take a stab at it?😉

 

I know I am close but I don't think I will be able to cross the finish line without some help. I went out today while it is 24° to see how it would start. Pushed to gas to the floor took my foot off the pedal and hit the key it cranked up perfectly. It does everything but run at wide open throttle.

 

I’m seeing 2/3 there.

So it’s a rich bog due to the rods lifting too soon and allowing more fuel than the engine/air flow needs?

 

Hmmm technically no. There aren’t any venturis in the secondaries. So, when the flap opens too quickly there isn’t any restriction of the air entering the throats. When they open at the correct rate that’s what pulls the fuel out of the jets past the metering rods and into the airstream.
In addition you’ll see two holes in the back of the choke horn that actually deliver fuel across the top to help in the transition of secondary opening. One of the many band aids GM added to the Qjet to make them work.

 

So does that create a lean condition? I'm getting confused about my level of correctness above.