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On a friends sbc he has a Holley 4 barrel with vacuum secondaries that open only about 10-15% at max pedal. What should I look for to remedy this and allow them to open to what I believe should be alot more? It's like he is running a 2 barrel. The linkage operates freely and by hand everything moves thru full closed to full open. I am not familiar with this style carb. Thank you.
 

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mrtimstik said:
On a friends sbc he has a Holley 4 barrel with vacuum secondaries that open only about 10-15% at max pedal. What should I look for to remedy this and allow them to open to what I believe should be alot more? It's like he is running a 2 barrel. The linkage operates freely and by hand everything moves thru full closed to full open. I am not familiar with this style carb. Thank you.

Are you sure they are not opening???? Normally vacuum operated secondarys will only open under a load. If you are trying to get them to open in the driveway with your hand/foot operating the throttle they will not open. So I guess the question is when you are driving down the road and punch the throttle do the secondarys open?
 

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Do the paperclip test to see if the secondaries are opening. Here's what Holley says to do:

The secondaries will not open by free revving the engine. The engine needs to be under a load before they will open. If you are still uncertain if they are opening or not you can take a normal paperclip and clip it onto the secondary diaphram rod. You will then push it up against the bottom of the secondary diaphram housing, now you will need to go out and drive the vehicle. When you return you will be able to look at the position of the paperclip on the rod. If it is lower on the rod then you can tell the secondaries opened and how far they opened. This is useful in determining if you need a heavier or lighter secondary spring.


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In the driveway, engine on, moving the linkage by hand to full throttle, it opened a very, very small amount. So I guess the paperclip deal is a clear indication of the actual stroke that takes place under the correct operating conditions. Now I have to figure out how to clip the paperclip correctly. Is there a diagram at the Holley site?
 

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I'm running vac secondaries on my truck's 327 Tom. He can either play with the dif rated springs OR I'd suggest getting an adjustable vac diaphram (an accessory) option kit. It makes tuning so much easier (like a Q-Jet), as the settings are then infinitely adjustable. They are not MADE by Holley, and I think I got mine through Jeg's. ;)

These are the folks that make em'...
http://www.quickfueltechnology.com/home_2.htm

Your buddy IS getting full linkage travel and achieving WOT, right?
 

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mrtimstik said:
In the driveway, engine on, moving the linkage by hand to full throttle, it opened a very, very small amount. So I guess the paperclip deal is a clear indication of the actual stroke that takes place under the correct operating conditions. Now I have to figure out how to clip the paperclip correctly. Is there a diagram at the Holley site?
I am also wondering if there is a diagram to make sure i am doing it correctly...my secondaries may not be opening at all - i fear my diaphram may be shot?
 
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