A very BASIC carb question??

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Jan 31, 2010 | 01:34 PM

MakoShark72

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Safety Car

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From: Gig Harbor WA

A very BASIC carb question??

Ok, this may seem a little basic, but.....

Holley SA 670..vacuum secondaries..

Primaries in the front, secondaries to the rear??? Right?

At WOT (engine OFF), WHAT should the secondaries look like?? Should the butterflies be open at all, when I look down in the throat??

When I move the throttle linkage full open (engine OFF), my secondary butterflies do not even move.

Is this correct, or do I need the engine running (hence vacuum) to open the secondary butterflies??

Thanks!
Rob

Jan 31, 2010 | 01:49 PM

yellow 72

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From: cincinnati ohio

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http://www.chevyhiperformance.com/te...ion/index.html

Jan 31, 2010 | 01:51 PM

midyearvette

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From: columbus oh

Quote:

Originally Posted by MakoShark72

you will not see the secondaries open when revving in neutral....read up on the holley adjustment procedure for the vac. sec. carbs....you can check it with some grease smeared on the diaphram rod or a paper clip, but you must drive the car...good luck

Jan 31, 2010 | 02:13 PM

MakoShark72

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From: Gig Harbor WA

Quote:

Originally Posted by yellow 72

http://www.chevyhiperformance.com/te...ion/index.html

Thanks, the secondaries DID open using the air hose method..

Quote:

Originally Posted by midyearvette

Where might I find the procedure? I suppose I could google it..

I guess the crux of my question revolves around new carpet, Dynamat, reflectix..... When the gas pedal is fully depressed, I just want to know that the secondaries are opening...is there a static way to check that?

Guess I should FIRST check throttle linkage movement when the pedal is depressed..

Thanks,
Rob

Jan 31, 2010 | 04:53 PM

427Hotrod

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Stomp it to the floor with engine off. The primaries will open all the way...and you will see there is a little bent link that rides in a slot on the secondary arm (driver's side of carb). While holding the throttle WOT....check to see that you can manually open the secondaries. The little link controls how far they can open in relation to the primaries. Might need to check choke linkage too to make suer it isn't holding them closed.

JIM

Jan 31, 2010 | 09:51 PM

lars

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From: At my Bar drinking and wrenching in Lafayette Colorado

There is nothing that can prevent the secondaries from opening other than a physical, mechanical blockage or inadequate throttle linkage travel. Venturi vaccum on the primary side will pull the secondaries open once mass flow through the primaries exceeds a certain point (which you cannot do under a no-load condition). You can make the secondaries open a little sooner by running a softer spring against the diaphragm, but rest assured that they will open, providing you have full throttle travel on the primary side (most C3 Vettes don't, due to carpet under the gas pedal or bent accel pedal linkage).

Lars

Jan 31, 2010 | 11:17 PM

MakoShark72

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From: Gig Harbor WA

Quote:

Originally Posted by 427Hotrod

Quote:

Originally Posted by lars

Thanks for the explanation! I understand the workings now.

And Lars...."bent accel pedal linkage" you are referring to, can be fixed by simply bending the linkage so the pedal sits slightly "higher" above the carpeting???

I just tested mine, and lo and behold I was NOT getting full travel at the carb. I slightly bent the linkage "up" (pedal is higher off the floor) and now the carb linkage goes full travel...

Just making sure I'm not missing anything here....

Thanks again,
Rob

Last edited by MakoShark72; Jan 31, 2010 at 11:31 PM.

Feb 1, 2010 | 09:30 AM

lars

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From: At my Bar drinking and wrenching in Lafayette Colorado

Quote:

Originally Posted by MakoShark72

And Lars...."bent accel pedal linkage" you are referring to, can be fixed by simply bending the linkage so the pedal sits slightly "higher" above the carpeting???

I just tested mine, and lo and behold I was NOT getting full travel at the carb. I slightly bent the linkage "up" (pedal is higher off the floor) and now the carb linkage goes full travel...

Just making sure I'm not missing anything here....

Thanks again,
Rob

That's exactly the issue, and that's the way to fix it - you'd be amazed how most C3 Vettes never get wide open throttle travel due to this problem. You simply bend the gas pedal and get 30 mmore horsepower...

Lars