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#1
03-17-2007, 12:05 AM
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Quadrajet question ?
What is the differences in the manual trans and auto trans carbs ? I am looking for a 73 manual quadrajet carb but they seem to be very high Thanks
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#2
03-17-2007, 01:05 AM
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For the most part,it's just #'s.
Stick cars were generally only about 20% of production,so they are far less common to start with. They were ALSO usually the first ones to get the Hedders & Holly kit (with yellow plug wires) so that makes them even LESS common. As I recall 73 & 74 Pontiac Q-jets are all pretty similar for linkage/hookups,etc. Unless you are stuck on the #'s, ANY Q-jet can be built/set-up for very satisfactory performance. (75 & newer get more complicated) |
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#3
03-17-2007, 09:52 AM
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Quote:
I think the only real differences in auto/manual might be in the tension on the secondary air valves and small differences in jetting as far as performance of the carb goes. Cliff would know I'm sure.
__________________
Uneasyrider “To find yourself, think for yourself.” ― Socrates “The unexamined life is not worth living.” ― Socrates “Wise men speak because they have something to say; fools because they have to say something.” ― Plato |
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#4
03-17-2007, 09:55 AM
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Also, the manual carbs don't have the vacuum port in the rear of the base plate, that would be run to the transmission vacuum modulator.
A simple plug at that location effectively makes an automatic carb into a manual with respect to external details. |
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#5
03-17-2007, 03:34 PM
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I beleive tha auto carbs had the hot idle compensation device on the rear of the carb also.
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#6
06-18-2008, 11:32 PM
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Hi TJH. I found that out when my mechanic used a manual quadrajet model on my TH400 GTO and hooked up the transmission modulator vacuum to the top port of the front driver side of the carb. I think that port is not "full manifold vacuum" as I have had shifting problems since. The bottom port on this carb is being used for the hideaway headlights. I am thinking of switching the two hoses top and bottom. if that doesnt work can you suggest an alternative site for the tranny modulator hose. Thanks
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#7
06-19-2008, 07:51 AM
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If I'm not mistaken, Mr. TJH passed away last year.
To answer your question, yes, switch those hoses. |
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#8
06-19-2008, 07:54 AM
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cushsix:
TJH passed away shortly after posting on this topic. If you notice, his post was in March of 07. He won't be responding to your question. Thought you should know!
__________________
Bob Woodard Brighton, MI 2012 SRT8 Charger - 12.70 @ 111mph |
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#9
06-19-2008, 02:19 PM
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Quote:
As far as difference in 73 manual tranny carbs..I just finished a '265 for a guy. There is a slight difference in the calibrations. But the biggest is going to be in the placement of the auto modulator vacuum port. The auto has it as I mentioned above and the manual doesn't. You can use a auto easily ,just plug the modulator line and have it built for your engine specs.I have done quite a few of the guys here on PY's carbs. You are welcome to PM me.I have a few '73's.I actually just bought a '73 auto tranny carb.I would be more than happy to restore it and sell it to you.. Just PM me.. |
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#10
06-19-2008, 07:06 PM
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I'm now confused. Everyone else has said you MUST run the trans modulator vacuum line to a FULL vacuum source, not ported. I have a M/T carb and it does not have a full vacuum source like the auto does. I currently have it plugged into the port you have indicated and the trans is not right. My carb is 7029263 I dont nknow what a "265" is. An auto would be 268.
Thanks |
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#11
06-19-2008, 09:53 PM
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Might be wrong on this, but if I recall correctly, Q-Jets don't have ported vacuum. In other words, no matter where you attach your vacuum lines, you get whatever vacuum the engine happens to be producing.
That's why the TCS solenoid was used (to cut out the vacuum advance at idle and the first two gears in a four speed as part of the emission control system), and (assuming your engine doesn't have the solenoid or it isn't working) that's why it is important to disconnect the vacuum line to the distributor before setting the initial timing. Having said that, I don't have a better answer to the problem with auto tranny, although I do suggest that the problem isn't where you attach the line (although if I recall correctly, the tee at the back of the carb was different for auto transmissions as it allowed you to hook up an additional line - the one for the transmission). |
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#12
06-20-2008, 12:52 AM
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My manual carb has a ported vacuum source on the left front lower part of the carb. My auto carb does not.
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#13
06-20-2008, 08:14 AM
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RWS, mostly correct but the transmission problem only started for me the day the mechanic installed a manual carb (263) and the trans modulator vacuum was moved to the carb. Were working on it to get the right place. thanks
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#14
06-20-2008, 08:15 AM
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Carcollector, Correct. and therein lies my problem Thanks
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#15
06-21-2008, 01:08 AM
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Quote:
I was wrong about the ported vacuum. The auto trannys vacuum port is "above" teh flaps, but it is a full vacuum source. Since you have a manual tranny carb, try sourcing vacuum from the rear vacuum "tree" where you get vacuum for the brake booster. That will be full vacuum and will make your tranny shift correctly. SOrry about thsi mistake earlier.. Good luck.. |
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#16
06-21-2008, 10:39 AM
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Quote:
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