Topic: 427 3x2 Carb Vacuum Spring Question.
in Forum: C3 Fuel, Emission Control, and Exhaust Systems
Already a Member?
Click Here to Login
Not yet a Member?
Click Here to Register for Free!
plasticpig said: Mike C.,
I have never had the vacuum pods opened on the carbs. I bought new replacements from the Chevrolet dealer in 1984 & had Holley rebuild and re-die before I took on the 50th Anaversity Caravan, (400 some miles of hot summer fun?).
I'm out of town till Saturday evening, but will check the old dealer parts books I have, they usually give a good breakdown of little items like this.
In the meantime, have you looked on the web, anything on Holley, not sure if they are reorganized?
PS, Your engine looks great, I should have mentioned that in the first reply!
Mike McElroy
Hello!
Thanks for the compliment on the engine! A bit of work on it and the carbs and the fuel lines to get it to look that way.
The factory springs as came stock in the Vettes was black in color. That is what I have read on various net articles. My particular car on initial inspection had two different springs between the front and back diaphragms!! Also, both rubber diaphragms were cracked and therefore leaked.
With Regards,
Mike C
SPONSOR AD:: (Our Sponsors help support C3VR)
plasticpig said:
As I understand it, the purpose of the spring is help in returning the center (primary) carb back to the idle position when you let off the gas pedal.
The Black spring would be for a 68-72 with a small block.
For the 69 Tri-Power the spring would be orange.
As long as your foot is heaver than what it takes to overcome the spring tension and the spring is weaker than the throttle cable, that part of the system will work.
The secondary's open with the vacuum diaphragms on each carb. (right side of the carb). The function of the linkage is to prevent the secondary's (carb 1 & 3) from opening at a low RPM, (vacuum surge).
Tried to post a photo of my spring which runs to the rear and is attached to the bracket that holds the throttle cable (mounts using the 2 bolts on the L side of the # 3 carb.) There is a small hole in my bracket. Yours may be correct with the little tab bracket on the #1 carb mounting bolt. Either way it's just to return the throttle to idle.
I'd check your linkage between the front and rear to the "throttle closing lever", (little arm out the L side of the secondary carb that controls the throttle blades, which are the 2 round plates in the carburetor bores.
With the engine off, (air cleaner removed etc.) you should be able to twist the by hand the bell crank on the side of the center carb (better yet is to have some help who will push the accelerator to the floor to make sure the center carb is opening all the way)!
Next is to adjust the linkage to the 1 & 3 carb., with the center carb in the idle (the engine is still off at this time!)
As memory serves twist the linkage to the #1 carb to where it just fits the "throttle closing lever" and then make one turn longer. Same with the rear carb.
Make sure you have good smooth operation of the secondary linkage connections where they connect to the primary (#2 carb), good plastic bushings, proper bolt and nut etc.
I drive mine very little but at about 4000 RPM it is a real kick in the seat when they secondary's kick in.
Mike
Hello Again!
An update on the carb discussion posted earlier.
I eventually weakened the vacuum pod springs on the outer carbs to a point where on the highway the outer butterflies were fluctuating open and causing very erratic cruising. I went to a two step stiffer spring and this seems to have remedied the issue. The current weather here cancelled any further testing.
As far as the rod linkage adjust to outer carbs is concerned, I have FINALLY purchased the 1969 Factory Assembly Manual. The procedure for adjustment is as follows. The rear carb linkage is attached to the center carb, then the linkage is extended till 1/2 diameter SHORT of the rod thickness, then attached to the rear carb throttle shaft. this adjustment will allow the rear butterflies to just slightly open. The linkage to the front carb is set at the center carb first, then extended till it reaches the CLOSED throttle shaft opening, then installed.
Still a work in progress!
With Regards,
Mike C
in Forum: C3 Fuel, Emission Control, and Exhaust Systems
SPONSOR AD: (Our Sponsors help support C3VR)