69 Quadrajet

[Bill C.]

I recently bought a 7029215 quadrajet for my 69 427/390 coupe. I disassembled it before installation and found there was no power piston retaining bushing. After installing the new bushing I have about 1/8" of power piston travel from closed to open. The question is...is that enough?
Primary rods are #45 and jets are #71...

[Clem Z.]

Re: 69 Quadrajet

I recently bought a 7029215 quadrajet for my 69 427/390 coupe. I disassembled it before installation and found there was no power piston retaining bushing. After installing the new bushing I have about 1/8" of power piston travel from closed to open. The question is...is that enough?
Primary rods are #45 and jets are #71...

the rods and jets are correct. there have been 3-4 different types of power piston retainers,which type did you use ?? i think the movement should be close to 1/4". maybe the lean stop has been changed. the assy length of the power piston should be 1.950 from the top of the hanger to the bottom of the piston. secondary metering rods should be AX

[Clem Z.]

Re: 69 Quadrajet

go here to check power piston adjustments. http://www.corvetteclub.org.uk/files...wer_piston.pdf

[Bill C.]

Re: 69 Quadrajet

Thanks Clem. The piston length checks out ok. I don't have a retainer, just added a new plastic bushing. When I compared this piston to the one that's in the carb currently on the car (7029201 Carter quad) I noticed the length of the top portion of the piston (smallest diameter where the bushing goes) was shorter on the 215. It's about 1/4" on the 215 and maybe twice that on the 201 (going from memory). With the bushing on that give's me that 1/8" of movement I talked about. I'm wondering if I have the wrong Piston for the carb? FYI...this carb came with AY secondary rods. I picked up a pair of AX size rods from Summit that I am using on the 201...I'll swap them when I put the 215 on.

[Clem Z.]

Re: 69 Quadrajet

Thanks Clem. The piston length checks out ok. I don't have a retainer, just added a new plastic bushing. When I compared this piston to the one that's in the carb currently on the car (7029201 Carter quad) I noticed the length of the top portion of the piston (smallest diameter where the bushing goes) was shorter on the 215. It's about 1/4" on the 215 and maybe twice that on the 201 (going from memory). With the bushing on that give's me that 1/8" of movement I talked about. I'm wondering if I have the wrong Piston for the carb? FYI...this carb came with AY secondary rods. I picked up a pair of AX size rods from Summit that I am using on the 201...I'll swap them when I put the 215 on.

the power piston the uses the plastic seal at the top had a small diameter length of .340 and the power piston that uses the other type of retainer the length is .220

[Bill C.]

Re: 69 Quadrajet

The Carter on the car has a bushing and a metal retaining clip. Is the metal clip what you're referring to? When I assembled the carb without the bushing the piston felt like it was binding a little, with it it feels smoother...and shorter. In looking at the body there's clearly an indent in the piston shaft for the bushing and I don't see any scratch marks that would have indicated the metal retainer??

[Clem Z.]

Re: 69 Quadrajet

The Carter on the car has a bushing and a metal retaining clip. Is the metal clip what you're referring to? When I assembled the carb without the bushing the piston felt like it was binding a little, with it it feels smoother...and shorter. In looking at the body there's clearly an indent in the piston shaft for the bushing and I don't see any scratch marks that would have indicated the metal retainer??

the later ones all used the plastic retainer/seal at the top with nothing else to hold in the power piston. the earlier ones used spring type retainer around the power piston barrel that went down inside the bore. i will post a picture later of the 2 types i have

[Clem Z.]

Re: 69 Quadrajet

the later ones all used the plastic retainer/seal at the top with nothing else to hold in the power piston. the earlier ones used spring type retainer around the power piston barrel that went down inside the bore. i will post a picture later of the 2 types i have

here is the type without the top seal/retainer

[Clem Z.]

Re: 69 Quadrajet

better picture with top seal/retainer

[Clem Z.]

Re: 69 Quadrajet

GM went to the top seal/reainer because dirt was getting into the piston causing binding with the power pistons without the seal. once GM did away with the external bowl vent were most of the dirt got into the carb the sticking power piston problem was mostly over

[Bill C.]

Re: 69 Quadrajet

Clem...great stuff...thanks. My piston is your 1st example although I don't have what looks like a metal clip in the center. Looks like I need to find one of those clips or the piston in your 2nd example that uses the bushing...any thoughts?
Bill

[Clem Z.]

Re: 69 Quadrajet

Clem...great stuff...thanks. My piston is your 1st example although I don't have what looks like a metal clip in the center. Looks like I need to find one of those clips or the piston in your 2nd example that uses the bushing...any thoughts?
Bill

i would stick with the power piston you have because i would guess it is the correct one. you don't need metal clip if you just use a small screwdriver to hold the piston down while you put the top back on. go here http://www.carburetion.com/quadrajet.asp and order part # 85-150 to hold the piston in place if you want something permanent

[Bill C.]

Re: 69 Quadrajet

Clem
Agree with the originality piece but I'm not sure if this is the original piston. I'm thinking they switched to the bushing type piston by 69 but I'm not positive. That said, the piston seems to move smoother with the bushing. I'm now leaning towards replacing the piston but I'm not having much luck finding one. I may have to go with the clip.
Bill

[Clem Z.]

Re: 69 Quadrajet

Clem
Agree with the originality piece but I'm not sure if this is the original piston. I'm thinking they switched to the bushing type piston by 69 but I'm not positive. That said, the piston seems to move smoother with the bushing. I'm now leaning towards replacing the piston but I'm not having much luck finding one. I may have to go with the clip.
Bill

i just checked my delco rochester parts book and it list part# 7034903 as the correct power piston for all the BBC Qjets 68/69/70/71.

[Bill C.]

Re: 69 Quadrajet

Is the 7034903 piston the one I have or the one I want?