Vacuum secondary spring question

[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.

[patrickt]

Originally Posted by 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.

No, that doesn't sound like they're opening fully. Here's how you tell. With the engine cool, use some string to tie your throttle back as if you were flooring the accelerator pedal. Then, push the zip tie's tail over so it's touching the throttle screw or whatever else is over there to stop it. Next, put your finger over on the bottom of the vacuum secondary plunger rod and push it gently all the way up in to the secondary housing, thus opening your secondaries fully. Take your finger off the rod and the secondaries close. View the position of the zip tie tail -- that is what fully opened secondaries look like. Now remove the string.

[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.