Q-jet Base plate's
Race Director
Joined: Dec 2004
Posts: 15,030
Likes: 2
What exactly are you looking for here, Russell? Shaft diameter? They are the same. Bore Diameter? That will change depending on the carb number. There are not too many CFM differences, but there are some.
Tell me exactly what you want and I will measure tomorrow. My brother and have a carb remanufacturing business here in Oklahoma. I have plenty of cores, plates, shafts etc.
One thing you need to do when pulling throttle plates. Rochester crimps the screws in place, and you need to grind the end flush with the shaft BEFORE you unscrew them. If not, it chews the threads. You can go with bigger screws, but it is a royal pain to deal with. Not a lot of room to be cutting new threads.
This is a fallacy.
Although there are shaft bores that have become oblonged(usually the result of too stiff of a return spring), bushing is not necessary in the majority of cases.
The main problem is the throttle plates have shifted slightly in the bores and will not close completely. If you look at the edges of the plates, you will notice they are beveled. Any deviation, and they will not fully seal in the bore. It is a simple process to reseat them. You just have to know how to do it. It is more of a visual thing, otherwise I would explain.
Tell me exactly what you want and I will measure tomorrow. My brother and have a carb remanufacturing business here in Oklahoma. I have plenty of cores, plates, shafts etc.
One thing you need to do when pulling throttle plates. Rochester crimps the screws in place, and you need to grind the end flush with the shaft BEFORE you unscrew them. If not, it chews the threads. You can go with bigger screws, but it is a royal pain to deal with. Not a lot of room to be cutting new threads.
It'd be nice to find a base plate that didn't need trottle shaft bushings..
Although there are shaft bores that have become oblonged(usually the result of too stiff of a return spring), bushing is not necessary in the majority of cases.
The main problem is the throttle plates have shifted slightly in the bores and will not close completely. If you look at the edges of the plates, you will notice they are beveled. Any deviation, and they will not fully seal in the bore. It is a simple process to reseat them. You just have to know how to do it. It is more of a visual thing, otherwise I would explain.
Race Director
Joined: Dec 2004
Posts: 15,030
Likes: 2
I will elaborate on this a bit more.
The reasoning given for bushing throttle plates is because there is movement when a person wiggles the throttle shaft. Must be sucking air, right?
Wrong. The main idle problems present are due to the plates not closing completely and the transitioning between drawing fuel from the idle circuit and the main jets. Other than the accelerator pump, the engine draws the fuel it needs through vacuum. If the plates are seated in their bores properly, the engine will draw the fuel it needs from the idle circuit.
If the throttle is closed and the plates are seated properly in their bores, there will be no movement of the throttle shaft.
There must be some clearance between the shaft and the housing. One is steel(hard) and the other is aluminum(soft). Not enough clearance, and the steel is going to gall up the aluminum. Then you have a housing that will need bushing.
The reasoning given for bushing throttle plates is because there is movement when a person wiggles the throttle shaft. Must be sucking air, right?
Wrong. The main idle problems present are due to the plates not closing completely and the transitioning between drawing fuel from the idle circuit and the main jets. Other than the accelerator pump, the engine draws the fuel it needs through vacuum. If the plates are seated in their bores properly, the engine will draw the fuel it needs from the idle circuit.
If the throttle is closed and the plates are seated properly in their bores, there will be no movement of the throttle shaft.
There must be some clearance between the shaft and the housing. One is steel(hard) and the other is aluminum(soft). Not enough clearance, and the steel is going to gall up the aluminum. Then you have a housing that will need bushing.
Race Director
Joined: Dec 2004
Posts: 15,030
Likes: 2
Shaft diameter .310
Shaft bore diameter .3125
Shaft length:
Early(remote choke) 6.750
Late(integral choke) 7.1875
There were only two sizes of throttle plates made. Cadillac, which had about 800 CFM, and everything else, which was around 725. Sorry, I forgot to get those measurements. If you are trying to put one in the other housing, it would be apparent you had the wrong part.
The shafts were all the same, except in length where noted above, and the arm attached.
The housings however were different. There are many different castings available and, while they may bolt up to the bowl, most are not interchangable. The majority of differences is in how and where vacuum {ported or straight) is drawn. There are casting numbers to match them with the application.
Shaft bore diameter .3125
Shaft length:
Early(remote choke) 6.750
Late(integral choke) 7.1875
There were only two sizes of throttle plates made. Cadillac, which had about 800 CFM, and everything else, which was around 725. Sorry, I forgot to get those measurements. If you are trying to put one in the other housing, it would be apparent you had the wrong part.
The shafts were all the same, except in length where noted above, and the arm attached.
The housings however were different. There are many different castings available and, while they may bolt up to the bowl, most are not interchangable. The majority of differences is in how and where vacuum {ported or straight) is drawn. There are casting numbers to match them with the application.
Thread Starter
Team Owner
Joined: Sep 2003
Posts: 88,393
Likes: 2
From: eville in
Originally Posted by nitronick
Shaft diameter .310
Shaft bore diameter .3125
Shaft length:
Early(remote choke) 6.750
Late(integral choke) 7.1875
There were only two sizes of throttle plates made. Cadillac, which had about 800 CFM, and everything else, which was around 725. Sorry, I forgot to get those measurements. If you are trying to put one in the other housing, it would be apparent you had the wrong part.
The shafts were all the same, except in length where noted above, and the arm attached.
The housings however were different. There are many different castings available and, while they may bolt up to the bowl, most are not interchangable. The majority of differences is in how and where vacuum {ported or straight) is drawn. There are casting numbers to match them with the application.
Shaft bore diameter .3125
Shaft length:
Early(remote choke) 6.750
Late(integral choke) 7.1875
There were only two sizes of throttle plates made. Cadillac, which had about 800 CFM, and everything else, which was around 725. Sorry, I forgot to get those measurements. If you are trying to put one in the other housing, it would be apparent you had the wrong part.
The shafts were all the same, except in length where noted above, and the arm attached.
The housings however were different. There are many different castings available and, while they may bolt up to the bowl, most are not interchangable. The majority of differences is in how and where vacuum {ported or straight) is drawn. There are casting numbers to match them with the application.
now i can start back on this mess
Pro
Joined: Jan 2004
Posts: 518
Likes: 0
From: oh
I have a couple of Cadillac Q-jets that I am not using if anyone wants them for the price of shipping. I think they are '67-'69's.
email me jjatich@hotmail.com
email me jjatich@hotmail.com
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