TLChydraulics: Different carb combos are a blast to mess with. For the "different" look it's hard to beat tripower or even the 2-4bbl Cross Ram (my favorite). Both are very streetable, and with the right tuning, can give you a gigantic "grin factor". And when you pop the hood...WOW!!! :eek: :eek:

Dep

 

Tom: The 4175 IS a bus carb! HA! Just kiddin :lol: :lol:

I agree that it's better to have the low rise than NO rise and no tripower. But I sorta wish Edelbrock would have made a high rise version just for some even better performance. I also wish I could AFFORD a tripopwer setup for my car. Cripes...need to win a few million dollar lotteries to buy that setup!!!!
:D :D

I vaguely remember that the GTO DID have vacuum secondarys. I think the ball bearing progressive linkage was a popular conversion for that car. But I'm an old fart and my memory ain't the best :)

Dep


[Modified by DJ Dep, 9:46 PM 4/8/2004]

 

I was toying with that idea, but could not find shorter bowls.....though the stock metering plates provide plenty of fuel at WOT

No
[/QUOTE]

 

George: See...told ya I was old and my memory was fading ;)

Found a tripower 1969 setup for rectangle port heads on E-Bay. Price right now is $700 and reserve is NOT met.
http://cgi.ebay.com/ebaymotors/ws/eB...472500348&rd=1


Expect it to go MUCH higher!!!
:crazy: :crazy: :crazy:

Dep

 

I've always liked multiple carb setups, starting with a '66 GTO 3x2. I also run 4x1 carbs on my Corvair Monza, and a 2x4 setup on a 409. The performance from a aftermarket manifold and carb (like a BG or Demon) will be better on a hot engine, but there is a definite "wow" factor to these multiples that can't be matched. The factory 3x2 on my vette was in bad shape when I got it, but with new linkage, lines and float bowls it now works well. My mileage is abysmal, but so what!

Boy, that 3x2 on e-bay is rough! No vaccum pots, linkage, air cleaner, or fuel lines and surface rust to boot! I guess you have to start somewhere, but that's a bit to much for me. Dep could give you a better idea on value, but there have been some fairly nice ones that trade hands for about 2K.

Hans


[Modified by Wrencher, 8:04 PM 4/8/2004]

 

Hans: Your mileage is bad because you keep OPENING those other carbs!!
:lol:

Dep


[Modified by DJ Dep, 10:03 PM 4/8/2004]

 

Hi Guys. I stumbled onto Corvette Forum yesterday in search of answers to a problem I'm having. I own a factory original '69 Corvette and am having a problem with the secondary carburetors not opening under full throttle on my 400 horsepower 427. The engine runs great but lacks the explosion of power that you would expect (and need!!!) from four more barrels kicking in when you mash the pedal to the floor. Looking down the throats, the butterflies don't move when I slam the linkage open. However I can manually operate them just fine with the linkage.

The engine is completely rebuilt and all three carbs were completely rebuilt and flow tested by the Holley factory as well. They are the original carbs that came on my Corvette and all hoses and linkages are properly installed. I have plenty of vacuum from the center carburetor base for the choke pull-off and for the vacuum advance but nothing from the port on the upper right side of the carb body where the hose connects.

I have applied vacuum from a hand pump to the diaphragms and they respond as they should.

Before I tear it back apart and disassemble the center carb, can you advise exactly where I should look for the problem? Perhaps an improperly installed gasket or ????? I'd rather not replace the unit or send it in for repair if I can locate the problem and fix it myself.


Thank you for your help


:confused: :confused: :confused:

 

Ron: Check your e-mail. I answered your letter. :)

Dep

 

The end carbs will not open by "punching" it when standing still.... the car has to be moving. The vacuum is not active until there is sufficient flow through the center carb which will not occur when "punching it" when sitting still.

Do this.... get a $10-$15 vacuum gauge if you don't already have one, and a long piece of vacuum hose to go from the center carb to the drivers seat. Hook up the gauge to the vacuum port for the end carbs.... take the car for a spin with the vacuum gauge sitting next to you or with someone holding it. See if you get a vacuum signal while driving it (hard).

If not, the center carb vacuum port is not functioning due to wrong parts and/or gaskets, or a blocked internal passage in the center carb.

Tom

 

Like to add one more thing to what Tom and Depster said: Could be the wrong springs are in the secondaries...if black spring is installed, then the secondaries will never open fully. If there is sufficient vacuum, then changing to a lightr spring will help

 

Tom,

Hmmm. I didn't think of that. I will try it. Still seems like I should get an explosive ammount of accelleration when I nail the throttle, though. Like a four barrel does only better. She goes alright and the torque builds as she accellerates. Maybe I just expect too much. :confused:

 

George,

You're right about the springs. I hear that they are available from Chicago Corvette Supply but I tried to find their website and can't. An artical I read says they sell them in a 3 spring kit, with different tensions on each. Any idea where else I can go to find them?

Ron :confused:

 

You can buy the springs from bob kuntz automotive in st louis. All he does is carbs for corvettes. He is in the corvette trader and hemmings. I had him resurface my secondary diaphram housings and went to a pupple spring and the performance improvement was dramatic.

 

You can try Summit, I believe all Holley vacuum secondary springs are interchangeable...you will need two kits...
Each kit contains a spring of different color, think there are 5-6 springs in each.

Be careful how you remove the diaphram screw, else it will get damaged.

Think Chicago Corvettes went belly up.


[Modified by GDaina, 11:29 AM 4/9/2004]

 

Thanks,

If Chicago Corvette Supply went Belly up somebody should tell Primedia and Vette Magazine cause that's where I read it in the June 2004 issue.

Thanks to all who answered. I wish I would have found this site about three years ago.

Ron :hurray:

 

Ron: One more thing you have to realize....
If you want "dramatic" openning of the front and rear crabs, you are gonna need a pretty wild gear in the rear end. If you are running a 3-series rear gear, you probably won't feel the carbs "snap open". I had a 4.10 in my Dodge, and from a rolling second gear punch at 30 MPH, it DID feel like a passing gear kicked in.

Dep

 

Michael,

She's completely stock. Running a 3.70 rear end ratio. It gets there pretty quick anyway. But, like everyone else I'm just looking for a little more. Everything I have read here makes sence to me. I just ordered the spring kits from Summitt. So.........we'll see. Stay tuned.
Ron

 

Ron: Sounds great! Keep us posted! :thumbs:

Dep

 

The GM BB Tripower diaphrams are larger than the typical 4V carb diaphrams, but I believe the springs are interchangeable as posted above. I just opened up a set and they look like the same physical dimensions as the TriCarb springs. They are color coded:

white- lightest
yellow short- lighter
yellow- light
purple- med light
plain (nocolor)- medium
brown- med heavy
black- heavy

There are 3 vacuum connections on the center carb:
1) The vacuum actuating port for the end carbs is in the main venturi, directly across from the high speed venturi, just below the main venturi transition point. You cannot see it looking down from above. With the throttle body removed, you can see it clearly from below. This port feeds directly to the nipple on the carb main body, and does not go through any gaskets.... so contrary to what I suggested above, a wrong gasket will not cause the port to
become inactive. There are no gaskets that can interfere with this port. It's also a fairly large port, so it is unlikely (although possible) that it will get plugged. However... there IS a small gasket between the secondary diaphram housings and the end carb main body- if this gasket is missing or faulty at either end carb, the vacuum signal will be lost, and NEITHER
end carb will open.

2) The Vacuum advance is PORTED as designed from the factory. I am holding a 2300 center carb throttle body in my hands at the moment...
On the passenger side bore, there are two ports visible above the closed throttle disc. One is slotted, (the idle to intermediate speed transition port), and the other is round... the PORTED vacuum port. When the throttle disc rotates past this port, air speed increases across it and creates a vacuum signal for vacuum advance. The connection is the nipple that exits the
throttle body (not the main body), perpendicular to the side of the carb. When the engine is running, and you "blip" the throttle, you will see a temporary vacuum signal at the nipple.

3) The other nipple exiting the throttle body (base) at an angle, is manifold vacuum, and is connected to the choke pull-off. The throttle body is machined on the bottom with a slot between this port and both throttle openings, below the throttle discs. Regardless of which gasket you use, this port will continue to provide manifold vacuum at all times. There is also a passage from this slot, up through the throttle body, and up into the carb main body. This
passage would normally pass manifold vacuum to an exterior port/nipple on the metering body.... but... correct GM BB TriPower metering bodies do NOT have this port machined in them, so it dead ends in the carb main body.

A common mistake is to install the diaphrams in such a way that the rubber is pulled inwards at the edge, causing a leak. This will also cause BOTH end carbs to stay closed because the actuating vacuum signal is lost. The trick is to hold the rubber diaphrams against the spring so they are relaxed when you tighten the housing screws, keeping ALL edges of the diaphram
properly located to avoid leaks and tears.

The diaphrams used to be available at NAPA. Holley part number 135-6.
The correct original spring is VIEW 37-1, index #74, 38R-477.

I don't have a cross reference to cross 38R-477 to one of the springs in the Holley spring kits.... someone at Holley would have to figure that one out.
38R-477 is the correct, original Holley part number taken from the Holley Illustrated Parts & Specs catalog for a LIST #3659 end carb, but don't expect anyone at Summit to comprehend that number.

Hope this helps a little.
Tom



[Modified by Tom454, 1:02 AM 4/10/2004]

 

I believe that is the medium non-colored spring.

Another method to install the springs....remove the diaphram housings, rest the bottom half across vice jaws and snug down the diaphram leg in the vice, make sure that the rubber edges lay flat and don't move, as per Toms post above. Now you can install the spring and the upper half of the housing...the vice will keep the diaphram from moving. You can protect the leg by placing it between two pieces of wood.