123+ and Idle Vacuum Advance

[jimk]

14 minutes ago, silasmoon said:

So since a hotter cam = less vacuum at idle, would I shift the initial vacuum point up from 45kPa to 50? I can take a reading after work today if I have a port on the manifold itself. 

That is correct, if your idle vacuum is less then increase the point upwards.  Move the next points up if needed also.

[silasmoon]

The manifold has no further ports on it for hooking up the 123 vacuum connection unfortunately. Is the port on the carb really not the correct one? I thought on a 38 DGES that lone port was indeed manifold. 

['76mintgrün'02]

Is the port above, or below the throttle plates?

It would not be hard to add a vacuum nipple to your manifold, if you don't mind drilling a hole in it.

Put it right below the carb, like on the stock manifold.

This post is sorely lacking photos, btw.

[silasmoon]

Here are some photos of the port I use on my carb. You can see it is to the top and right of the idle mix screw. 

 

[jimk]

That port in the pics appears to be the one for a vacuum pot on the distributor and won't work well with the settings I gave.  it has no appreciable vacuum at idle, the most vacuum occurs at slight to moderate throttle then falls off at higher loads.

A pure manifold vacuum port would have high vacuum at idle, decreases as load increases and falls of at hither loads.

You would have develop the pressure values for that port or if someone else has worked them out would share with you.

The pics seem to show an after market manifold and why no other port.  The cast in bosses could be drilled, tapped for 1/8"NPt and a brass adapter installed for a manifold port.

Edited June 1, 2017 by jimk

[silasmoon]

Hrmm, that seems doable. I saw that a lot of people just vacuum / magnet out the shavings, but thats on exhaust manifolds. I suppose I need to yank the whole thing off to tap a port?

['76mintgrün'02]

I would be lazy and drill a much smaller hole, for a friction fit on a little brass tube, the size of the one on the carb.  No tapping threads, just tapping the tubing in with a little hammer... and a wooden block, to protect the brass.  You could also just tap it in there with a little jb weld, if the fit was not dead nuts.

 

I would drill it in place, knowing no chips will be going inside the manifold until the bit comes through.  Those last two chips will probably get screwed out like the rest of them.  I like the central location, right under the carb.  That is the place I have my manifold gauge connected.  

 

If you drill there and are paranoid, you can pull the carb and watch the drill come through, then clean up the mess that probably won't happen.  It is good to be careful/certain.  Taking the carb off would also let you be sure to drill into a thicker part of the casting.  A photo might give you that info though.

 

I would like to chop those extra bosses off of the extra manifold I have. Those are for threaded attachments of emissions vacuum gizmos and such, which I don't have a use for.... yet.