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how can I tell if my secondaries are working? When I stomp on the gas I hear the roaring and get the extra pull but i figured that was the downshifter.
 

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You can google to see how to put a paper clip lightly on the secondary linkage, then drive it and see if the clip moves or gets kicked off. I think you can also take the carb off, open the primaries, and use an air compressor hose to blow air through the primaries while watching the secondaries.

Pat
 

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So when people say "I could hear those secondaries kick in," they might be imagining it?
 

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if the carb is working correctly, you would never feel the secondaries open. there would just be a steady pull through the rpms
 

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alot of gm s had quadrojet carbs that wern't set up correctly and the would make the quaaaadrojet sound
 

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Yeah, just a steady pull. They come in gradually so that's the reason for no accelerator pump on the secondary side except for mechanical secondaries.

With mechanical secondaries, you might feel the added tension with your foot. At least you can with tri-power setups or with dual quads. You can feel the extra force required to open them.

Pat
 

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There should be more intake noise when the secondaries open and the kick in the pants from the downshift should feel like a kick not a pat on the a$$. If the secondaries don't open the acceleration when passing would be pretty lazy compared to a properly functioning carb.
 

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What type of Carb is it? Vac Sec are suppose to come on evenly with no lag. Mech can cause a bog if the carb is to big or RPMs are to low. They both are adjustable.
 

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Interesting post - my 390 is pretty pedestrian when you get your foot into it - there is no discernable increase in acceleration above about 2,500rpm, it's just a slow increase with lots of noise and no 'go'.

The carb is a Holley 600 VS so I might check this out - I've already had to replace the accelerator pump diaphragm due to it leaking so maybe the diaphragm for the vac sec's is also leaking...
 

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As an input, I have never seen the secondaries NOT work when someone asks these questions. A little tongue in cheek, but the alternative is to disconnect/lock them and see the difference as well.
 

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Interesting post - my 390 is pretty pedestrian when you get your foot into it - there is no discernable increase in acceleration above about 2,500rpm, it's just a slow increase with lots of noise and no 'go'.

The carb is a Holley 600 VS so I might check this out - I've already had to replace the accelerator pump diaphragm due to it leaking so maybe the diaphragm for the vac sec's is also leaking...
2 things to check on it, remove it and compress it, then put your finger over the hole and it should stay in place. If it does, check your spring color and go with lighter spring.
 

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Discussion Starter #13
Is there a way to snake a tube onto the vacuum pickup and apply some suction?
 

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Just take it off and suck on it. It's easy and it works. Forget the puns and just do it. If you do take it apart to check the rubber diaphragm, be very careful putting it back together. Get the screws wrong and you can ripe the diaphragm.
 

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Had to dig it out, (old tech article from the early 70s). There is 2 vacuum ports that feed the dashpot. Pri & Sec. When you remove the Dashpot, look at the hole that supplies vacuum. To the back of it, there is a hole that has a steel ball in it to seal it. That plug is where they drilled the port to the Pri Venturi. Is you look in your Vac supply hole you'll see a hole that goes toward the Sec venturi. That one needs to be plugged. Put a 1/8" steel or lead shot into that hole and drive it in using a 1/8" punch. What this does, is block off the vacuum single from the sec and uses the primary side only. This will give you a quicker signal. The port to the sec bleeds vac in and slows the signal to the dashpot. Did it to my 780 and 600 and makes them respond much quicker.
Tried to scan the article but my scan didn't want to talk to my puter. Hasn't had it's 5th cup of coffee yet I guess.
Took a picture of an old one I had setting around. This shows the port I'm talking about.
 

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Discussion Starter #16
I have a Ford 4100 carb. What Dashpot?
 

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that was about a holley. your secondary diaphragm is centered in the back with a lever coming out of the pass.side
 

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on the 4100 with the air horn off, behind the rear float bowl there are three holes. 2 are to hold the air horn on .the center hole is where the vacuum is applied. put a hose over it and suck. make sure the throttle plates are open so the secondary lock out is disengaged
 

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Love these types of posts asking for help. "My green car won't start, any ideas"? 10 posts down , oh and by the way it doesn't have a battery, engine or gas in it either.
 
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