Need Detaled Picture of 427 3x2 Carburetor Linkage

[Jacob A.]

Hello,

I have the picture from the 1967 Corvette Assembly Manual.

In regards to a 67 L-71 Tri-Power....

Does anyone have a more detailed picture or the real deal in close up. My engine is supposed to hit the dyno this week, and my engine builder is having a problem hooking up the linkage that was sent from my parts vendor.

Thanks,
Jacob

[Tom H.]

Re: Need Detaled Picture of 427 3x2 Carburetor Linkage

Hey Jacob.

Here's one I found. I'll try to find you a better one.

[Jacob A.]

Re: Need Detaled Picture of 427 3x2 Carburetor Linkage

Thanks Tom,

I will send the link to my engine builder.

Very Best,
Jacob

[Jacob A.]

Re: Need Detaled Picture of 427 3x2 Carburetor Linkage

Successful Mission!!!! Thanks so much! My engine builder was able to make heads from tails based on your pics Tom.

All systems are now go, and the engine will be dyno'd very soon!

Very Best,
Jacob Angel
NCRS # 40987

[Tom H.]

Re: Need Detaled Picture of 427 3x2 Carburetor Linkage

Good deal. Glad I could help out !

[Wayne M.]

Re: Need Detaled Picture of 427 3x2 Carburetor Linkage

Jacob-- what you need (even more so than pictures) is a detailed description of the adjustment procedure. This was printed in Dec '67 issue of Chevrolet Service News, and does include a picture. Did your (repop ?) linkage kit supplier also provide these instructions ?

I can take pics of the CSN procedure article, and close-ups of my late '69 linkage hooked up to my center carb [but not the ends], if this might help.

[Cory A.]

Re: Need Detaled Picture of 427 3x2 Carburetor Linkage

I can take pics of the CSN procedure article, and close-ups of my late '69 linkage hooked up to my center carb [but not the ends], if this might help.

Ohhhh, please post. I just had my carbs rebuilt and l'd like to see how the linkage goes back together. Somehow I misplaced my mental picture. Please post the CSN too, thanks.

[Robert K.]

Re: Need Detaled Picture of 427 3x2 Carburetor Linkage

Wayne,

I would like to see the CSN article and the picture too (if you would be willing).....


Thanks Wayne,

Bob

[Jacob A.]

Re: Need Detaled Picture of 427 3x2 Carburetor Linkage

Thanks Wayne, That would be fantastic!

Very Best,
Jacob

[Wayne M.]

Re: Need Detaled Picture of 427 3x2 Carburetor Linkage

OK guys -- sorry I'm late.

First two thumbnails are the Chev Service News article (bottom of first column on the page, and top of 2nd column).

Third pic is of my late '69 L68 set-up. Carbs & manifold are just sitting on the heads of a block on an engine stand in my basement. At least there are no fuel lines blocking the view . I have the rod to rear carb first on the center connector (clevis) pin, then the front [this might be the in the wrong order, but I have no tri-power AIM to confirm, or to know for sure whether I'm missing another washer/spacer on the center carb clevis pin (it's a little sloppy now). 1967 has slightly different rods due to use of a throttle rod (vs. throttle cable) and changes to geometry of fuel lines.

In principle, the rods act only as a safety backup, in case the outer carbs stick open when the vacuum falls off. Here's a paragraph from a '67 Chev carb booklet:

" ... a model 2300C is mounted as a primary in the center of the intake manifold with two model 2300's mounted fore and aft. The secondary carburetors do not contain chokes, accelerator pumps or power enrichment systems. The secondary throttles are actuated by primary carburetor vacuum. Low vacuum, such as occurs on full throttle or with abrupt throttle openings, overcomes the spring pressure in the secondary throttle diaphragms. High vacuum, present under part-throttle conditions, allows the diaphragm springs to close the secondary throttles."

[Jacob A.]

Re: Need Detaled Picture of 427 3x2 Carburetor Linkage

Thanks a bunch Wayne. I have forwarded the information to my engine builder. We both certainly appreciate it.

Very Best,
Jacob

[John H.]

Re: Need Detaled Picture of 427 3x2 Carburetor Linkage

"The secondary throttles are actuated by primary carburetor vacuum. Low vacuum, such as occurs on full throttle or with abrupt throttle openings, overcomes the spring pressure in the secondary throttle diaphragms. High vacuum, present under part-throttle conditions, allows the diaphragm springs to close the secondary throttles."

Gotta love that (incorrect) Chevy description of how they're actuated .

Manifold vacuum (which that paragraph describes) has nothing to do with the system. The secondary diaphragms are actuated by venturi vacuum, not manifold vacuum. As air velocity increases through the center carb venturi at open throttle, an increasing vacuum signal is created at the pickup tube (think Bernoulli's principle), which is routed to the diaphragms, opening the secondary carbs. As the center carb throttle closes down, the air velocity drops, so does the venturi vacuum signal, and the springs in the diaphragm housings close the secondary carbs.

[Jacob A.]

Re: Need Detaled Picture of 427 3x2 Carburetor Linkage

Thanks John!

[Wayne M.]

Re: Need Detaled Picture of 427 3x2 Carburetor Linkage

Gotta love that (incorrect) Chevy description of how they're actuated . ....

John -- correct you are . Rather than quoting the words of the Brochure, I should'a taken a pic, that includes a schematic of the vacuum lines. This shows the vac source from the center carb venturi (not the manifold, which is the only way [some of their] description makes sense).

But then, true to form, they show the outboard vac pods with the spring on the wrong side of the diaphragm (as shown, under venturi vacuum or not, throttle plates would always be open).

Must'a been an early publication, as the outboard bowls show vents.

[Howard P.]

Re: Need Detaled Picture of 427 3x2 Carburetor Linkage

Wayne

Thanks very much this information is very informative

Howie