Too much power too quickly with 8 barrels !

[Luke427]

While I could agree with the last statements, there's been some interesting findings there - secondaries not behaving correctly resulting in terrible engine response, dangerous for regular drivers and uncomfortable for advanced drivers.

Jumping from 20% to 100% throttle over half an inch pedal throttle and 500 RPM isn't what one should expect, especially with 560 hp

[Gaz64]

That certainly is a problem in how the secondary barrels operate.

I don't know how long since the last carb rebuild.

I would suggest feeling what each secondary shaft feels like as you open each set of butterflies from closed to open.

Wedge the primaries to wide open throttle once, and check the secondary barrels.

If you have a binding shaft or both, then the carb bases may be warping slightly.

I absolutely hate any thick gasket without any crush limiting spacers.

If the secondary vac chambers don't have the check ball, that's part of the problem.

Can we see what springs are fitted?

[Tim7139]

Originally Posted by Luke427

While I could agree with the last statements, there's been some interesting findings there - secondaries not behaving correctly resulting in terrible engine response, dangerous for regular drivers and uncomfortable for advanced drivers.

Jumping from 20% to 100% throttle over half an inch pedal throttle and 500 RPM isn't what one should expect, especially with 560 hp

Point taken, thats more of an "anybody that dares drive this thing" kind of problem I guess.

[DanEC]

Originally Posted by Luke427

While I could agree with the last statements, there's been some interesting findings there - secondaries not behaving correctly resulting in terrible engine response, dangerous for regular drivers and uncomfortable for advanced drivers.

Jumping from 20% to 100% throttle over half an inch pedal throttle and 500 RPM isn't what one should expect, especially with 560 hp

That definitely is not how Holley vacuum secondary 4 bbl carbs are designed to operate. Although it's commonly stated that vacuum instantly drops to zero when the throttle is matted (usually when talking about vacuum advance), that's not accurate as far as what the carb is seeing internally. There is residual vacuum depending on engine size, rpm, load and carb size. The residual vacuum (my term - not sure what carb designers call it) will fall gradually as engine load and rpm catch up to the primary air flow capacity and as determined by the vacuum secondary spring, the rear throttle plates will then begin to open. From that point on it's a balancing act as the demand for more air keeps pulling vacuum lower and lower and pulling the secondaries further open against the spring pressure.

The mechanical linkage sounds typical - not actually sure if it's primary purpose is to prevent early opening of the secondaries, to ensure closing of the secondaries on lifting off the throttle or both. I would pull the carbs, get a good Holley book at the book store and see what you have inside the vacuum secondary pods. Possibly a check valve ball is missing in them or something. Or, could just need a heavier spring to slow their opening down.

[patrickt]

Vacuum secondaries are controlled by venturi vacuum, which is directly related to the speed of the air/fuel mixture going past a small hole, which produces the vacuum. Put manifold vacuum completely out of your mind when thinking vacuum secondary action. You can test this operation, and your secondaries, with your air compressor, and the engine not running. Just blow air past the hole to create the "vacuum." Here's a short how-to, with pics: Holley Vacuum-Secondary Operation - Tech Article - Chevy High Performance Magazine

[Luke427]

Thanks folks.
I need to manage a couple more urgent issues with another car then I'll get back to the Cobra, and will fix these carbs

[Cobranut]

Originally Posted by fordracing65

If I had a wife she would never drive my cobra. Even if it was Danica. It's kind of like saying your bazooka has to much kick for your wife to shoot. Get her a 22 cal or a Miata.

Bazooka's don't recoil...

[patrickt]

Originally Posted by Cobranut

Bazooka's don't recoil...

I once blew a bubble with Bazooka gum that, when it popped, astounded me with the recoil.

[Mother]

Use a throttle stop. The lady will get use to the carb set-up