Quadrajet rebuild kit advice

72ray

72ray

72ray
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1972 coupe 350 TH400
It appears that the power valve in my Quadrajet has failed. Car coasts along fine but any sudden, hard acceleration (eg over-taking) causes immediate dead spot and it’ll immediately loose power and just roll along at idle until it recovers.
That said the model number on the Quadrajet reads 7045626. Looks like a 75 carby has been put on my 72. Having trouble identifying a rebuild kit for THIS EXACT carby
Or even just a power vale for now. HELP!
 
72ray said:
It appears that the power valve in my Quadrajet has failed. Car coasts along fine but any sudden, hard acceleration (eg over-taking) causes immediate dead spot and it’ll immediately loose power and just roll along at idle until it recovers.
That said the model number on the Quadrajet reads 7045626. Looks like a 75 carby has been put on my 72. Having trouble identifying a rebuild kit for THIS EXACT carby
Or even just a power vale for now. HELP!
Click to expand...
If you have ever had a Quadrajet apart, this might work for you. Rather than try to explain it myself, I found this

Many years ago I had a '68 Firebird with a Qjet. About once a year the power piston would stick in the down position.
I used a wire coat hanger with a ground down end and made a hook on it.

Just run it down the vent tube and hook the hanger, and give a little pull.
It will likely be a bit snug.
I then take a screw driver and push it back down. It will likely stick again.

Keep repeating the process until the piston can be pushed down and it will spring back up with no resistance.

After that, every few months, take a screw driver and bounce it a few times.
it shouldn't stick again.

Permanent fix is to remove the top of the carb and remove the piston and slightly hone the bore with very, very fine sandpaper.
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But if you don't know what the power piston looks like, might not be a good idea. Back when I took these apart all the time, this method saved me taking the top off the carb one time. My bible at the time was a Rochester Carburetor book by Doug Roe. In it he described how to make a 'key' shaped tool to go down the vent tube and free up the power piston. Worked perfect, but I think a perfectly bent coat hanger would work. Don't yank up too hard. Pull hard enough, you can pull the arm out of the piston. Like it says above. Give it a little pull. If it doesn't move, push it down a little. This method does work, but you have to have an idea what the hanger on the top of the power piston looks like. You could always take the top off the carb. That's how I learned. Trial and error. If you do it on the engine be REALLY careful with the 2 little screws down the primary bore and the one on the secondary needle arm. Drop one and you are then gonna learn how to take the intake manifold off. Q-jets used to be really plentiful. Actually in a pile at an auto wrecker. If you could get a spare to play with first, you would be an expert in no time. It isn't rocket surgery. A Rochester book helps but just to take the top off, free up the power piston and put it together, not really necessary. The top gasket can be reused. If you tap the pin out on the accelerator pump arm, remember to put something the width of a screwdriver against the intake horn so the pin will bottom out on it instead of the intake horn. Then you have the space you need to get behind it to pry it back in later. It's a huge PITA if you don't. Too bad you didn't live closer, I would pop over and show you how. It would take a wee drive to get to you.

Bic
 
turbozig said:
Great writeup @Bixter44. I have rebuilt many carburetors but wasn't sure how to go about starting to explain this. 👍👍
Click to expand...
Honestly, I didn't know where to start either. When I found that other write up, I stole it and pasted it. But then it seemed that once I got going I couldn't shut up. I had to just quit talking. It's hard to explain it alright.
 
72ray said:
Get this..... I put a little light weight oil down the shaft of the accelerator pump with the hope that it may cause the rubber seal on the piston to swell up and temporarily fix this. It worked beautifully! 😳
Click to expand...

Pretty slick MacGyver move @72ray! Please keep us posted on how it holds up at this point in through the summer.
 
Will do. I’ve managed to get hold of a kit to put through it (not as easy to find down under as in your part of the world) but finding the time is a factor for me atm. 👍
 
The ‘MacGyver’ move worked for the month. It did buy me more than enough time to find a carby overhaul kit and have it shipped so yesterday the overhaul began. During reassembling I’m having some difficulty with the choke linkages. No surprises there!
 
Can Anyone describe how the lower (internal) end of the primary choke flap linkage connects to the lower linkage down inside the body? 🤦🏻‍♂️
 
72ray said:
Can Anyone describe how the lower (internal) end of the primary choke flap linkage connects to the lower linkage down inside the body? 🤦🏻‍♂️
Click to expand...
OK, I looked on You Tube real quick hoping to see something that would help. Nothing helpful there on a quick look. It's been 30 years but I think I know what you want help with. It involves a short slightly bent rod with two short 90 degree bends in it at each end. If not forget I said anything. :)Anyway, you lower the rod down to the linkage you have to hook up to, only you lower it down sideways to the way you need it to be when you are done. This should be between the body of the carb and the wee arm with the hole in it down inside the carb. When you get the end of the rod even with the hole in the linkage, turn the rod towards the hole and it will go in there and stay there as long as the rod stays aimed in that direction. When you hook up the linkage on top of the carb it will. Hope this helps. Been a long time. I wish I still had a Quadrajet to go look at for a memory jogger. All I am sure of is that there is linkage on there somewhere that need this procedure done.
 
Yes what you’re suggesting sounds correct. I just can’t see down in there to tell if there is a hole in the lever as you described that the rod slips into. I’ll keep trying. In the exploded diagrams I’ve found I can’t see any hole. 🙏
 
Started 2nd crank, took it for a drive and it goes like a rocket. Only issue was the secondary air flaps/choke not opening up on hard acceleration (AKA tunnel mode). Temporary fix by disconnecting vacuum relay that holds them shut. TBC but happy for now.
 
CAFBBE20-1212-4078-8848-0841EBEA6F9C.jpeg
 
Yeah you’re correct. My problem is that it was warmed up plenty and it’s only the primary choke that’s controlled by the temperature controlled spring. My problem was the secondary choke flaps. I expected the vacuum controlled relay that holds the secondary choke flaps shut to relax from a drop in vacuum when I opened the throttle ie there’s next to no vacuum with an open throttle. Apparently not! I could feel it wanted to go under hard acceleration but was big time starving for air. I Couldn’t simulate it in the driveway though the secondary choke flaps were definitely locked shut. So I disconnected the secondary choke relay from the vacuum source and plugged it. Drives like a rocket! Hmmm
 
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