I have a Holly 750 (ish) vacuum secondaries on top of a 400 Small Block. When I floor it, it goes good, but I think it should deliver more pull than it is. I popped off the K&N cleaner to view the secondaries. When I slammed open the throttle, the engine rev'ed, but the secondaries didn't budge. I removed the diaphram assembly and sucked on the opening. It held a vacuum and the shaft connected to the diaphram moved correctly.
1) If I slam the linkage to WOT for 2 seconds, is that enough time for the secondaries to move?
2) How can I ensure a vacuum is getting to the diaphram?

Little Help???
Jim
71 El Camino & 71 SS 454 Chevelle

The secondaries for your carb will not open up while the car is parked. They only open under engine-load.

Chances are they are opening, just too slowly for you to feel it. You need to get a 2ndary spring kit for your carb. Install the second from the "lightest/easiest" spring and see how you like it.

If it bogs, go stiffer.

You can rig up some kind of a "trip-wire" to see if they are in fact opening. Use something like Solder (wire) and fix it below the linkage. If it's bent out of the way after running it on the road, they work.

Also, try fixing them CLOSED with that same driver's side linkage. Then do a back to back, seat of the pants test. http://www.chevelles.com/forum/smile.gif that'll be the easiest way.

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71' 3880# with me. Big Block 402, Merlin oval heads, 10.2:1CR, TH400, 3.73 posi,
1/8th: 8.0 @ 88mph
1/4: 12.5 @109mph w/ 1.89 sixty foot (street tires)
Picture of me roasting the tires and other guy stuff (http://www.auburnextremeracing.com/drivers/mike/)
My other site, picture oriented (http://www.chevelle-ss.com/Member's_Pages/Mike_S.htm)

-Heart of Dixie Chevelle Club www.chevelle-ss.com (http://www.chevelle-ss.com)

It's a common misbelief that you should "feel the secondary's kick in". What you're usually "feeling" is the bog when they snap open, until the engine can actually use the additional fuel. Like BB-Mike said, pick up the "Quick Change" kit at the speed shop, find a deserted road, and experiment. It's reasonably cheap, and be sure to keep track of the little *&#$^% O-ring that usually falls off when you do the conversion.

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"Atomic Batteries to Power...Turbines to Speed"

(The Minnesota John D)

'64 El Camino
383 - TH-350 - 12bolt - 4wh pwr discs
Bedded down for the Winter.

The last Holly I rebuilt with a holly trick kit had the litle cork gasket that went in between the body and the diaphram. It had adhesive on it to make sure it stayed in place. They say you shuld replace it when ever you pull the diaphram housing off.

BTW if you can hold your throttle WO for 2 seconds and get away with it a lot, I want to know who builds your engines.

Will

D) All of the above.

Great ideas guys! I tried the soldering wire trick (a few time) and it showed the Vacuum Secondaries were "not" opening. Then I disconnected the Vac Secondaries and it did "not" make a difference. It's looking as if my origonal suspision was correct....the secondaries aren't opening.

But...check one other thing. I wanted to check to ensure the throttle cable was giving the full travel to the carb. Guess what I found....Ya....when I had somebody push down the pedel to the floor (engine off of course), there was a good amount rotation still left in the carb linkage. Now I'm thinking the secondaries aren't opening because the carb isn't opening all the way.

When I get back home today, I'm going to adjust the throttle cable to get 100% travel at the carb and see if that makes the secondaries open.

I'll let you all know how it goes!

Desert Heat
71 El Camino and 71 SS Chevelle 454

That would be true of your primaries, but your secondaries should open as the engine demands it, not based on pedal position.

Try a lighter spring in the secondaries, go 2 sizes lighter than you have now.

Bingo! The vacuum secondary's "are" opening.

I got a Vacuum Secondary spring kit as you all suggested and used the short yellow spring (2 steps lighter). The instructions said it was the lightest, but the white spring felt lighter to me. It "did" ran stronger, but I was using the "soldering wire" trick that BB_Mike suggested and wasn't sure it was giving conclusive data.

Soooooo.....check this out: I have a web camera laying aroung my office. I plugged it in to my laptop and instantly I had a small color camera with a 10 foot cord to my laptop. I taped the camera to the valve cover and a little mag light shining on the linkage. I hopped in the El Camino and Wow! Very Cool! I had a perfect real time streaming video of the linkage and yes, the secondaries were opening around 3000 RPM. Problem solved thanks to you guys!

Desert Heat
71 SS454 Chevelle & 71 El Camino

[This message has been edited by Desert Heat (edited 12-01-2002).]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Desert Heat:
I have a web camera laying aroung my office. I plugged it in to my laptop and instantly I had a small color camera with a 10 foot cord to my laptop...<HR></BLOCKQUOTE>

That freakin' ROCKS!
I'm still laughing that you tried the Solder trick. http://www.chevelles.com/forum/biggrin.gif good stuff.



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71' 3880# with me. Big Block 402, Merlin oval heads, 10.2:1CR, TH400, 3.73 posi,
1/8th: 8.0 @ 88mph
1/4: 12.5 @109mph w/ 1.89 sixty foot (street tires)
Picture of me roasting the tires and other guy stuff (http://www.auburnextremeracing.com/drivers/mike/)
My other site, picture oriented (http://www.chevelle-ss.com/Member's_Pages/Mike_S.htm)

-Heart of Dixie Chevelle Club www.chevelle-ss.com (http://www.chevelle-ss.com)

I went through the same thing a few years ago, and rigged a micro-switch to the slotted linkage on the end of the throttle shaft. It would light a LED I put in the face of the tach. My damn mileage went in the toilet! I was alway wanting to see "my cool little light" come on! http://www.chevelles.com/forum/biggrin.gif

PS, I later reused the switch and a relay to trip a plate NOS cheater system @ WOT.

Hey! How about a little video clip of your secondaries in action??!! I think that'd be cool!
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'64 El Camino
383 - TH-350 - 12bolt - 4wh pwr discs
Bedded down for the Winter.

[This message has been edited by John D (edited 12-02-2002).]

Great idea with the video