Vacuum secondary spring question

[Rick Parker]

Testing for WHAT??
Beige paint, two roll bars covered with insulation on hundred year-old Yokomas---testing for low ET to the laundromat???

That there is some funny s*it.
I use that stuff on my water pipes in the Winter

[DanEC]

I'm still waiting for a picture of the zip tie on the shaft. I know Patrick has one. I may try the zip tie trick myself.

[patrickt]

The first picture shows the zip tie in the normal setting when the vacuum secondaries are fully closed. The shaft will rotate within the zip tie itself as the secondaries open. Then, when the secondaries close back up, the zip tie will remain in the same position on the shaft that it held while in the fully open position. How far the secondaries are opening is then readily apparent. The second pic shows how the zip tie appears when you get back home after the secondaries have opened completely during your "test drive." Note: I took these photos with the zip tie tail "extra long" so it would show up better on the photos. You trim the end of the zip tie so it is as short as possible (like maybe an inch or so -- just enough to touch the idle screw).

[genolan]

Originally Posted by patrickt

The first picture shows the zip tie in the normal setting when the vacuum secondaries are fully closed. The shaft will rotate within the zip tie itself as the secondaries open. Then, when the secondaries close back up, the zip tie will remain in the same position on the shaft that it held while in the fully open position. How far the secondaries are opening is then readily apparent. The second pic shows how the zip tie appears when you get back home after the secondaries have opened completely during your "test drive." Note: I took these photos with the zip tie tail "extra long" so it would show up better on the photos. You trim the end of the zip tie so it is as short as possible (like maybe an inch or so -- just enough to touch the idle screw).

How tight should the zip tie be and why wouldn't the secondary shaft spin in both open and close directions and not move the zip tie at all, Or move it when it opens and move it back when they close.

[patrickt]

Originally Posted by genolan

How tight should the zip tie be and why wouldn't the secondary shaft spin in both open and close directions and not move the zip tie at all, Or move it when it opens and move it back when they close.

The zip tie should be "handshake tight." That means tight enough to stay put on a rotating shaft, but loose enough that the shaft can rotate within it. When the secondaries open, the shaft rotates in a counter-clockwise direction. The zip tie rotates normally along with the shaft, but it is stopped by the throttle screw, so the shaft continues to rotate "inside the zip tie loop." But when the secondaries close, the shaft just rotates back clockwise and the zip tie stays fastened to the shaft in the exact same position. The zip tie will always register the maximum amount that the secondaries opened during a test run.

[jhirasak]

The nice part about a Holly with vacuum secondaries is that the secondaries only open after you have sufficient air flow through the primaries. When adjusted properly you should not have any bog during acceleration and they only operate when the engine demands more air flow than the primaries can provide. As a result, they are more economical on fuel than a Holly with mechanical secondaries. Under WOT acceleration, if you install a small screw in the slot of the mechanical linkage between the primary and secondary shaft, you will assist the opening of the secondaries while the AFR is still slightly rich due to the accelerator pump shot. This is why a four barrel with vacuum secondaries are more suitable for street applications.

[genolan]

Originally Posted by patrickt

The zip tie should be "handshake tight." That means tight enough to stay put on a rotating shaft, but loose enough that the shaft can rotate within it. When the secondaries open, the shaft rotates in a counter-clockwise direction. The zip tie rotates normally along with the shaft, but it is stopped by the throttle screw, so the shaft continues to rotate "inside the zip tie loop." But when the secondaries close, the shaft just rotates back clockwise and the zip tie stays fastened to the shaft in the exact same position. The zip tie will always register the maximum amount that the secondaries opened during a test run.

Thanks that makes perfect sense!!

[DanEC]

Originally Posted by patrickt

Thanks - I had it in my mind you were fastening it around the vacuum canister rod so that the tie slid along the shaft as the rod was sucked up into the canister. I'll give it a try.

[patrickt]

Originally Posted by DanEC

Thanks - I had it in my mind you were fastening it around the vacuum canister rod so that the tie slid along the shaft as the rod was sucked up into the canister. I'll give it a try.

Short of all-out 100% racing, vacuum secondaries are, in every way, superior to mechanical secondaries. Their only downsides are you have to get them adjusted just right for full enjoyment. Just remember, the vacuum is venturi vacuum -- and the only way you create that is by hard acceleration. Chas' posting above is partly in jest, but more truth than not. In order to really set it up properly you have to get on it as hard as you can. When you do, there should be no detectable bog, you shouldn't be able to "feel" anything, and when you check your zip tie, it should show that everything opened up as far as they will possibly go. Unless you have an airport runway nearby, it's a rather dangerous test.

[ERA Chas]

Originally Posted by patrickt

Chas' posting above is partly in jest, but more truth than not.
Unless you have an airport runway nearby, it's a rather dangerous test.

No, not jesting. Actually, one exit on the parkway or the luxury of the beach road on a weekday was a frequent and easy way to get 'load'.
Did it weekly on the Connecting Highway or 231 as a callow (but talented) youth.
Certainly the dragstrip or autox course is more ideal. Hell, Bruce in 3170 gets that in first gear but I'm sure he does not have nancy vacuum secondaries...

[genolan]

I used the zip tie and it showed a 45 deg rotation. I was under full throttle in third gear at about 3800 rpm. Is this in line with expectation? Under what condition should I see a full 100+ deg rotation. I had no bog and currently am running the long yellow secondary spring. I could only punch it for a few seconds since the road was short.

[jhv48]

Originally Posted by patrickt

Short of all-out 100% racing, vacuum secondaries are, in every way, superior to mechanical secondaries.:

Say what? Even Holley and Edelbrock don't recommend a vacuum secondary carb for our light weight cars!

[patrickt]

Originally Posted by jhv48

Say what? Even Holley and Edelbrock don't recommend a vacuum secondary carb for our light weight cars!

Only because the secondary spring rate is more difficult to nail on a light weight car. But once you've done it right, it's superior.