427/435 Tripower secondaries operation

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Aug 15, 2005 | 12:43 PM

427VET

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Intermediate

Joined: Aug 2005

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From: Brentwood NH

427/435 Tripower secondaries operation

Hi folks, I have a 69 435/427 that I was playing with yesterday trying to see if the secondary carbs were working. I put some vacuum to the "T" for the outboards with the throttle linkage actuated wide open(engine off) for the mech. linkage slot. It wouldn't open the secondary throttle blades. So I pulled off the vacuum pods and checked them and they open with vacuum applied. But when I bolt them back to the carbs and apply vacuum to the carb fitting it doesn't work and I can hear a vacuum leak inside the carbs. Isn't it supposed pull open the secondarys just by applying vacuum to the fitting or is there an additional vacuum tap inside the outer carbs that supplements the signal from the center carb? The seal was good between the vacuum pod and the carb body.

Last edited by 427VET; Aug 15, 2005 at 01:01 PM.

Aug 15, 2005 | 01:01 PM

427VET

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Intermediate

Joined: Aug 2005

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From: Brentwood NH

test

Aug 15, 2005 | 01:19 PM

griffths

Racer

Joined: Dec 2002

Posts: 421

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From: Long Grove, IL

As you have suspected, there is an internal vacuum bleed between the vacuum pod and the carb so using someting like a Mite-Vac hand pump will not work. Snapping the throttle open while in neutral will not work either since there must be some load on the engine before the secondaries will open. The easiest was I know of to see if the secondaries are opening is to put a paper clip on the rod between the butterfiles and the vacuum pod right under the vacuum pod then drive the car making sure that you drive it in a way that the secondaries should open ("drive it like you stole it"). If the secondaries are working the paper clip will be lower on the rod then before you went for a drive.

Regards,

Jay

Aug 15, 2005 | 10:06 PM

Solid LT1

Le Mans Master

Joined: Dec 2003

Posts: 5,727

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From: Fremont CA

The Holley 2300 carbs have a internal air bleed that will probably not allow you to use a Mity-vac stlye pump to open them. These bleeds are plugged by knowledgeable Mopar Six Pack Drag racers (and I'm sure the Chevy guy's do it too.) I'm sure you know the carbs are locked closed with a mechanical linkage too that unless you open the primary carb to WOT will prevent them from opening. I went through H*LL with my old 440 Six Pack to get it into the 11 second zone before Mopar Super Stock racer Paul Rossi showed me the secret of making a Six Pack run by plugging the air bleeds during a NHRA meet at Fremont Drag Strip many years ago. You may also want to look into the new "jet plate" for the outboard carbs that allows you to put std Holley jets into the outboard carbs instead of the miserable jet plates and those PITA gaskets. The "Jet Plate" has been released in the last year or so, it would have made my life WAY EASIER in the good (?) old days.

Aug 16, 2005 | 06:14 AM

427VET

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From: Brentwood NH

Hey guys, thanks very much for the info. Solid LT-1, can you tell me where the air bleeds are located and how you plugged them? It doesn't make sense to me why they would put an additional tap inside the carb- inside the venturi won't see a signal until the throttle blades crack, which won't happen without a signal to the pods. And if the tap is under the throttle blades the vacuum pods would open at idle. Must be a little more complicated like a simple mechanical vacuum switch to accomodate both taps and open the carbs. Appreciate any info on it. My 65 GTO runs in the 11's N/A with 3 rochester carbs but I have aftermarket mechanical linkage on those. It also has a 250 shot plumbed for those times when you need a little more...