I'm Trying to ajust secondary carbs and I need to know if the the plates need to be closed fully after rods are in place? When I put the rear linkage into place they say it should be short half the rod dia. If this is done it seems to open the rear carbs plate slightly. The engine runs fine but the center carb idle ajustment is completely unscrewed. I have no experience with tri-power set ups and any sugestions would be helpfull.
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Re: L-71 carbs ( secondaries).
The end carbs need to be closed at idle. The function of the linkage is actualy to CLOSE the end carbs when throttle is released, they are opened via vachume. The end carbs also do not have any provisions for an idle circuit. all idle adjustments should be made to the center carb w/end carbs closed. Hope this helps.
Dennis -
Re: L-71 carbs ( secondaries).
Hi Trebor:
I am afraid I have to dissagree with Dennis, the Assembly manual as well as numerous other documentation states EXACTLY what you were led to believe, the REAR secondary carb linkage should be adjusted 1/2 a rod diameter short of entering the hole In effect opening the rear throttle plates slightly. My 69 runs perfectly adjusted in this method and if I close the rear plates, (as one would think natural) I loose the ability to adjust my primary carbs idle and end up with a unmanagable erratic idle,the oppsite of what you are experiencing. You failed to mention your primary jet size, it is possible that you may compensate by changing those jets to obtain an acceptable metering plate adjustment. It sounds as though you have bypassed the idle circut entirely. Good luck JerryComment
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Re: L-71 carbs ( secondaries).
Jerry,
The jet sizes are "63" . The car idles nice with rear linkage rod disconnected.Do you install rear linkage with center carbs throttle at normal idle position or with plates completely closed? I do believe your right about the rear carb being partially open. Why put the rear rod short?Comment
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Re: L-71 carbs ( secondaries).
Jerry,
As I and wayne have posted, proper center carb adjustments CANNOT be made with secondary carb plates open. These tri power systems operate very similar to a standard vachume secondary holley 4 barral. If your car needs to have the secondary carbs cracked open, you are adding additional air to compensate for a problem elsewhere. Often on these systems the carbs develop an internal fuel leak that creates a need for additional air. The secondary carbs do not serve any purpose on idle and you should be able to make tuning adjustments to your car with the secondary carbs return linkage disconnected. I think that many people misunderstand the function of the secondary carb linkage and assume it s to open the carbs, it is not. It is designed to ensure the secondary carbs do not remain open after you let off the gas.
DennisComment
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Re: L-71 carbs ( secondaries).
I am only repeating what knowledge I have acquired through research of past printed material supplied by both Chavrolet, and Holley,and that experience gained by owning seven Tri power eguipped Corvettes. My carbs are restored by Jerry Luck Motorsports, they have all flat surfaced decked, and all shafts have been line bored, they function perfectly and idle consistantly at 900 RPM, I understand the linkage function completely and as a simple test of the proceedure described by Wayne my rear secondary is minimally open and drawing air when adjusted in this fashion, as further conformation I called Jerry Luck (341-895-1551 and this is the adjustment proceedure he uses on his own cars (and the end result is the rear secondary is slightly open)and he finds both idle and throttle response to be "As good as it gets". I am sure others have different adjusting methods and different degrees of success but I repeat I only replied with what works for me and I do understand the system
JerryComment
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Re: secondaries on 3 X 2, and single four barrel
My understanding of my single 4 bbl vacuum secondaries (from Holley's procedure and setup) is that you close the secondary throttle plate, THEN open it a very small amount via the adjusting screw for that purpose. This amounts to turning the screw 1/4 turn from the position where the plates are fully closed.
This is supposed to help the transition when the secondaries start to open, by allowing a very small amount of air flow. This has miminal affect on the idle mixture, which is handled by primary screws. I believe the 3 X 2 principle is the same.Comment
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Re: Tripower secondaries rods adjust
Wayne,
Placing rear rod short opens the secondary. You would need to make it longer to keep it positivly closed. I will try agian tonight. Thank you for your help.Comment
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Re: Tripower secondaries rods adjust
Good point about the difference in throttle openings between secondaries on a single four vs the 3 X 2 setup with the 1/2 rod adjustment. Indeed, if the rear carb throttle is open very much at all, it will cause problems. I will be needing all this info pretty soon, as I will be having Jerry Luck (hopefully)restore my 3 X 2 setup. I will probably need all the help I can get. This forum sure works well for this kind of info sharing! EverettComment
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Re: Tripower secondaries rods adjust
Wayne,
That makes sence, However, the rear rod does not move independently. If the rear rod moves forward to close rear secondary the front rod must follow. If the front is completly closed then the rod won't move foward and the rear secondary will have to open to place in rod. I'm going by what I see and I just went and looked again. Thanks again, with everybody's input I'm sure to figure this out.
Trebor MelickComment
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Had the same problem- Solved it.
Listen guys I had the exact same problem. I bought a tripower car that had been stood for 18 years, had the carbs restored and then tried to adjust them as per AIM and workshop manual. I tried for days but whatever the rear carb stayed open a fraction and then whatever you do you cannot set the idle on the primary. In the real world I found that you adjust the rod so the rear carb is just closed. You can then set the idle and everthing works fine.
Best of luck SteveComment
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Re: Had the same problem- Solved it.
Steve,
Today I drove car for first time. I have the rods set to what the AIM said. The car ran ok and idled fine but I do think it could be tweaked some more. Are you saying "to close rear carb completly" or open just a hair.
TreborComment
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