I'm running the 390cfm Holley 4bbl.
How do I tell if my Vacuum Secondaries are opening? I don't think they are...I just don't feel them come on...and the throttle plates are dry and charcoal colored.

Soupitup@msn.com

Good to see that I am not the only one who has had this concern.
The *best* way to check this is to get the car onto a chassis dyno and do some "pulls" while you watch.

Next best is the dragstrip test. I go to a test and tune session with a handfull of the secondary springs and start tring different ones, the time clock tell the story.

Here is another "trick", I mounted a microswitch onto the carb that comes-off the secondary linkage, it is wired to a small light on the dash which comes-on when the secondaries start to open. (I can also trigger my NOS system off this switch)
This tells you the secondaries are open but you have to keep re-adjusting the switch's position in a "hit or miss" fashion to figure-out how far the secondaries are opening.
(My current SL6 has a hard time completly opening the secondaries on the 600 cfm Holley it's running)
DD

If the carb is tuned properly you won't feel them opening. It is supposed to be a smooth transition.

That being said; what color secondary spring are you using? The stock natural color spring is stiff (intended for a small v8) and will not allow the secondaries to start openig until quite high in the rpm range. I am using the long yellow spring which is a little to soft (I can feel the secondaries open) but I like the sensation. The purple is likely the best bet.

If you follow Holley's recommendation you keep going softer until you get a bog then go up a size or two.

Dave

Hot-Rod 6
dave.clement@motorola.com

Dave, Doc,
Thanks for the quick reply. I have installed the Quick Change spring kit form Holley and have gone through the spring progression and settled on the brown spring.I have since found out that a trick way to check the travel is to put a paper clip on the diaphram rod (top next to housing) then make a run. Check to see how far the clip slid down the shaft.I Have'nt tried it yet but I'll let you know how it works.It just bugs me that I can't tell. Doc: I like the Idea of a micro switch because it gives you a constant monitoring...so that you know exactly when it opens.
Also I want to try putting a screw through the safty cam on the sec plate shaft. I thing this could be adjusted to make sure they are fully open at full throttle...but experiment will tell.
Thanks again I'll let you guys know what happens.

Trysix/David

Soupitup@msn.com