C3 Tech/Performance V8 Technical Info, Internal Engine, External Engine, Basic Tech and Maintenance for the C3 Corvette
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Old May 13, 2022 | 08:53 AM
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Hello All,

I have a 1980 C3 with L48 and new top end. I'm trying to dial everything in but I find that power surges once secondary opens up. I made sure that butterflies were opening when engine was warm and found that the power would somtimes pop in other times it wouldn't. I then pulled back secondary primaries (top ones controlled by vacum) and power was always there when I stomped on it but it initially bogs like it's flooded? Not sure what adjustment or what I should check can be made improve the situation.

I've heard that Lars will do carb rebuild so not sure if that is necessary. Car runs fine on primaries just intermitant once secondaries open up.

Thanks
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Old May 13, 2022 | 11:37 AM
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Google Quadrajet secondary air valve adjustment and set the tension to 3/4 of a turn from closed.
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Old May 13, 2022 | 11:49 AM
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Good advice. Also, make sure your secondary airvalves are not binding or sticking against the airhorn casting along their rear edges.

Lars
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Old May 13, 2022 | 11:50 AM
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Originally Posted by MelWff
Google Quadrajet secondary air valve adjustment and set the tension to 3/4 of a turn from closed.
Thank you!
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Old May 13, 2022 | 12:20 PM
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Originally Posted by lars

Good advice. Also, make sure your secondary airvalves are not binding or sticking against the airhorn casting along their rear edges.

Lars
Lars,
Do you recommend that before making the adjustment, air doors closed rotate the slotted shaft so the pin in main shaft just makes contact with the loop of the spring before making adjustment?
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Old May 13, 2022 | 12:28 PM
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Originally Posted by bmotojoe
Lars,
Do you recommend that before making the adjustment, air doors closed rotate the slotted shaft so the pin in main shaft just makes contact with the loop of the spring before making adjustment?
in case he doesn't answer soon, the 3/4 setting is from the point where you already have enough tension against the spring to hold the door fully closed so in order for that to happen the pin would have to be in contact with the spring.
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Old May 13, 2022 | 01:14 PM
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Originally Posted by lars

Good advice. Also, make sure your secondary airvalves are not binding or sticking against the airhorn casting along their rear edges.

Lars
I opened butterflies and did notice just a bit of resistance when it starts to open. Got a rag with some carb cleaner and cleaned edges and that did the trick. What a difference.

Thank you.
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