[mike's 68]

Hey guys need to know which port to use for vaccum advance. The port on metering block or base plate.1968 327 30 over 11.5 to one
327/350hp GM cam

[camnut]

metering block

[snake]

All the replys i ever got all said baseplate full vacume is the best.

[gheatly]

A ported vacuum source such as the metering block provides NO vacuum at idle. A ported vacuum source is designed to provide a vacuum signal at a pre-calibrated engine speed. Ported vacuum sources are generally used on late model cars to operate emissions equipment.

Manifold vacuum, on the other hand, is a function of engine load (less load = more vacuum = more advance).

You want the vacuum advance to work at idle or under light throttle, high vacuum situations such as cruising. This being the case, you will need to connect the vacuum advance to a manifold vacuum source.

I just finished reading "Super Tuning and Modifying Holley Carburetors." Isn't it amazing how much you can learn by reading the right book?

[kz1000ltd]

Hey Gheatly, why don't you help me rebuild by 750 DP? I think it's the power valve that went bad, but it's probably best to go through the whole thing while I've got it apart.......I've got a rebuild kit on the way.......what do you work for, money or beer?

[CarlC]

Gene,

Send me the book that shows me how to stop throwing money at my car.

------------------
Click here to see see my car and hear 5-speeds. http://www.geocities.com/casanoc

[mike's 68]

Thanks guys Sounds like i need to move the vaccum to the base of the carb. One more ?
On a vaccum carb like this I can not tell if
the back barrels are opening while reveing the engine by hand & looking at the butterfies. Any suggestions??? This is a new carb. The old one was monofied with a set screw to manualy open the rear butterfiles at full throttle. thanks guys

[Go69]

Your secondaries should not open unless the engine is under a load and you have the primaries open far enough that the linkage will allow the secondaries to open. If you have the car in neutral and you are under the hood revving the motor-they should not open. Someone on this site once before posted the same question and if I recall correctly the way to test for secondary operation is to take the car for a full speed blast (off of public highways). Then wire the secondaries so that they can not open and take another blast. If the car slows down on the second run you know your secondaries are working. If it runs the same on the second run, you know you have some adjustments/tuning/repairing to do.

[wwind]

On a Holley with vaccum secondaries they will not ( should not ) open just by revving. the engine needs to be under load. What I do is take a ordinary paper clip and slide it over the rod from the vaccum pod to the seconday throttle plate. The clip should be able to slide on the rod with some friction. Move the clip up the rod to fit against the bottom of the vaccum pod. Take the car for a good run to open the secondaries. Stop the car and check to see if the clip has moved down the shaft. If it has the secondaries opened. You can tell how far by opening the throttle ( engine off ) and pushing up on the secondary rod to where the clip touches the bottom of the vaccum pod. If no travel is left they opened fully, however this does not always mean the best performance. To change how much they open, you need to experiment with different springs in the vaccum pod.

[mike's 68]

Thanks Guys. The info you gave will help alot We will try them this week if we can get a spare min, or two.
Thanks MIKE'S 68======== == =

[gheatly]

KZ,

I'll work for beer. Just bring it by some weekend and I'll help you with it. I have rebuilt several Holley carbs and feel I am pretty good at it. I'm still learning how to tune though.

I think most problems with Holley's can be traced to the fact that most people don't take the time to sit down and learn how they actually work. The Holley design is really very simple, once you have read the book 2 or 3 times! I have only been tweaking carbs for about a year and am just starting to get comfortable with what I am doing.