[Joe]

I have an extra set of end throttle bodies. With the thick blades. Yet no bleed holes in them. My other set does have the bleed holes. I want to drill the bleed holes in the set that currently does not have them. I have read 2 posts where 1 says .026 and the other says .030. Which is most accurate?
Thank you

[Kenth]

.030" give or take .001" is what i have seen thru the years.
What is the size on your set with the holes?

[Joe]

Thanks for the reply,
My set with the hole's measures .029(-) gauge pin as a clean pass through.
Using a .030(-) pin it goes almost all the way through.
So it looks like they agree with your numbers.
Thanks Again

[Jack Gifford]

I'm not onboard- why would I want to create a vacuum leak?

[Rich-Tripower]

Without air bleeds in the outboard carbs, the vacuum signal when running only on the center carb can get real strong and pull the outboard carbs open some amount thus opening them before you want them to be open.

[Hotrodfarmboy]

I'm in agreement with Jack. Why creat a vacuum leak. Also, isn't it vacuum that holds the outers shut and a lack of vacuum that opens them ??? This is why I have always preferred manual linkage over vacuum. Wait a minute, I gave it more thought and it's the springs that hold them shut and ported vacuum that opens them. If manifold vacuum is opening them you need stronger springs.... I ��

[Hotrodfarmboy]

And yet another silly thought popped into my brain.... why would GM use DAG213 to seal the throttle blades and then drill a hole in them to cause a leak ????? Seams like two steps forward and then two steps back. And also, if manifold vacuum was high enough to pull the secondaries open wouldn't the vacuum then drop and the springs would close them ???

[Kenth]

I wouldn't go so far as to say that these small holes would cause a vacuum leak. And they can't be compared to worn edges on the throttle blades or rusty throttle plates that require DAG123.

I have understood it to mean that the holes in the throttle blades are there to evacuate residual fuel vapors after Pontiac switched to the unvented gasket between the throttle plate and the float housing, so that the residue wouldn't stick to the throttle blades. And as such the holes are a part of the calibration.

FWIW

[Hotrodfarmboy]

What you are saying is true for a center carb but to me makes no sense for an outer carb. My understanding of the extra hole is this: It allows the throttle blades to be fully closed and still gives air into the engine at idle. Without the holes the blades would have to open slightly but this would uncover the transition slots causing a rich mixture and making the idle mixture screws ineffective. To have the holes in the outer carbs makes no sense to me. Why do they use the block-off plates to tune your center carb if the outers are a factor in the calibration ? I have seen the quote "engineers do things for a reason" a zillion times but I have seen cases where engineers do stupid things too 🤔

[Kenth]

"Why do they use the block-off plates to tune your center carb."

Who are "they"?

I´m sure none of the engineers behind the Tri-power system did this, nor the factory releasing the cars for the public.

Holes in center carb throttle blades is another story not related to the holes in the end carbs throttle blades.
Most, if not all, A/T center carbs have these idle bypass air holes to keep the thottle blades in correct position to the off-idle circuit holes/slots, while the M/T center carbs did not need the idle bypass air holes.

And, NO Tri-Power will run with the center carb throttle blades fully closed.

[Hotrodfarmboy]

you're right, I should have said "some people" instead of "they" Thanks for pointing out that it was different for auto trans and manual trans. I was not aware of that.