1ARACE

I'm looking for suggestions and/or ideas, as to why the outboard carbs will not open up. This is what i've done so far:

I've read through this:
http://www.corvettefaq.com/c3/tripower/

...and this:
http://www.corvette-101.com/vacuum.htm

...and I am still not finding a solution as of yet...so i'm all at this point.

Quick background:
-All 3 carbs were rebuilt from Holley.
-No apparent vacuum leaks (headlights, wiper door, distributor vacuum advance, brake booster, etc.. function normally). Pinched off hoses to double check...no change in RPM.
-Ran compression check, all cylinders equal.
-Pulled plugs, nothing noticeable, rechecked gaps.
-Pulled carbs, used new gaskets (correct gaskets for center and outboard carbs).
-Checked for leaks around carb bases via spraying WD-40 around bases, no RPM change.
-Put paperclips on vaccum pod rods to double check if they engaged during runs under load, no movement.
-Idle is steady/normal (950rpm).
-Auto choke working properly.
-Vacuum hoses are connected correctly and tight between the three carbs.
-Outboard butterflies open/close freely, and close completely via one-way linkage.
-Float level is set at the bottom threads of the plug holes and correct.

Is there something simple i'm overlooking?

Thanks

__________
www.youtube.com/69Stingray427

TheSkunkWorks

You may have done so without mentioning it, but I didn't see where you've tried tuning the secondary vacuum diaphragm springs under load. If that's the case, I urge you to do so because of the three BB Tri-power setups I've had over the years none has yet to perform properly without my taking this vital step. Just keep putting weaker and weaker secondary springs in until it bogs under load and back up to the last previous set. If it doesn't bog with the weakest springs, leave 'em in.

TIPs: Ignore what they do sitting in the driveway when you goose the throttle; it's what they do while your actually driving that matters. And, by all means, resist the temptation to make the secondaries manual.

The only Holley secondary diaphragm spring kit I know of available nowadays is # 20-13, and yes you'll need two.

Here' hoping your problem is this simple...

WESCH

Hi

Did you emntion if you tested this opening of the 2ndaries during driving the car ?
They will not open with the car static even at 6500 RPM, only open under load during driving.

With other words, if you can pull on the highway in 4th gear over 5000 RPM, they do open.

Günther

1ARACE

After catching a few nice days I took the vette out for some tuning, and i'm still not so sure the outboards are opening.

According to this:http://www.corvettefaq.com/c3/tripower/ they 'should' open above 4000 RPM.

I held it to the floor, took it up a little above 6000 RPM and I still did not feel any 'kick in the pants' past 4000 really, it seemed to accelerate smoothly all the way until I let off it. I'm a bit nervous to keep it that high in RPM for too long, since it's the numbers matching motor and only about 800 miles on it since rebuild, but I just want to be sure the outboards are 'actually' working.

I put paperclips on the vacuum pod rods again to see if there is movement, but they are either popping off from vibration or possibly they are opening and knocking them off...i'm really not sure. Is there another way besides paperclips that works well?

I was thinking...could the fact I have a M21 close-ratio with either 4:88/4:56 gears, play a factor in them opening?
Or, I read this somewhere not sure where, could it be something to do with how tight/loose the air cleaner is, ie. air flow between the three carbs?

Thanks

________________
www.youtube.com/69Stingray427

TheSkunkWorks

You really need to test different secondary springs to know you've got the opening rate dialed in. And, that "kick in the pants" is commonly the surge of power coming on after a lag (tho not necessarily a bog) once the fuel delivery catches up to secondaries which have opened prematurely. It has been my experience that a properly setup tri-power delivers a steadily growing crescendo as opposed to a radical sudden burst...

BTW, the air cleaner's flow rate significantly effects 3x2 setup. Run the freest flowing one you can, or stick with the stock oiled foam piece.

ti9ere

Hi
i just read your blog about the tri power with the non opening secondaries....it didn't see an ending but I have the exact problem.....identical!
How did you sort it?
many thanks , Paul

fogaley

Try this, unhook or plug the front and rear carb vacuum lines and go drive the car. Note the sound, its ability to rev, how it pulls under acceleration. With the lines plugged you know the front and rear are not opening.
Now hook the lines back up and go drive it. Are the performance parameters different.
There is a big difference in the way the motor performs with the 3x2s hooked up and unhooked.
Scott

3X2

Is the vacuum hose to the secondaries connected to the correct fitting on the primary carb? Should be the one next to the choke pulloff and not manifold vacuum. Do the throttle blades open if you use a mityvac on each carb? Maybe "t" a vacuum gauge to see if there is a vacuum signal to the secondaries while driving.

ti9ere

Hi Scott
Thanks but sadly I'm way past proving they do not open - even to the point of visually confirming it on rolling road test! They 100% do not!
I'm still at a loss!!
Thanks anyway...

ti9ere

HI
Yes done all this but thanks. The mityvac test doesn't work unless the port inside the venturi on the F/R carb is blocked, and then yes it does proving the diaphragm and the linkage works. Also yes I'm connected to the correct port, even then I did try connecting to manifold vacuum and again this proved the secondaries work given enough vacuum (can't drive like this though and you can't accelerate below 3000rpm)
Thanks anyway....