Vacuum source?

[Ricks56]

My '56 312 has a '57 distributor and a Holley Performer 2 bbl carb on it. This conversion was done before I got the car. The distributor vacuum is connected to a ported source from the carb. Is this correct or should it be connected to manifold vacuum? Thanks.

[dmsfrr]

Yes, the ported fitting on the side of the carb is where it should connect.
Does the timing advance seem like it's not working correctly?

[Ricks56]

Not sure at this point. The port on the carb only gets vacuum when the throttle opens. The engine seems to be sluggish until the mechanical advance kicks in. I am going to try it with the manifold vacuum and see if there is any difference.

[dmsfrr]

If the vacuum diaphragm on the distributor has a hole in it, or the plate the points are mounted to doesn't move, it won't work either way. That could be the problem.
The oem connection was to the port on the carb.
If the distributor is out of the car or the engine isn't running, an easy but slightly distasteful method of checking the vacuum canister is to hook a longer piece of tubing to it and suck on it to see if the points plate moves.

The '57 to '59 points plate rotates on ball bearings around its outer edge. After all these years they often need to be thoroughly cleaned and lightly lubed.

[Ole Don]

If the distributor is an unknown, it may have dirty insides. Take it apart and clean out the old hard grease, put in some new lube, make sure the plate moves easily on the rubbing blocks. If you don't feel up to doing it yourself, contact Bubbas Ignition in Indy. He does a great job for a reasonable cost. Y blocks respond well to more initial advance than the book calls for.

[Ricks56]

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I will put a timing light on it sometime today and see if the vac advance is working. My main problem is I was reading on the internet (everything is true on the internet don't you know!) about the arguments of using manifold vac vs ported vac. I always thought that an increase in vac to the distributer canister advanced the timing. Someone made a good case for why you should use manifold vac and suggested that high vac retards the timing. Do some distributers work differently than others in this regard? I'm pretty sure my old '57 Chevy was using manifold vac.

[dmsfrr]

There was a thread here a couple months back with some 'discussion' about using ported or manifold vacuum for distributor timing advance. (someone was banned)

- IIRC - the general agreement was: ported vacuum works better for normal use with oem type parts on stock or nearly stock engines.
Manifold vacuum can work well on one-off setups, esp. with non-oem carbs & camshafts for more modified / performance engines.

Unless you're running some custom setup the way I look at it is... if Ford, Holley & Autolite hadn't thought ported vacuum was the thing to do they wouldn't have gone to all that time and expense to design and build the parts that way... or have used that system for so many years/decades.
.

[Ricks56]

Agreed. I wasn't trying to start WWIII. There is info out there on direct acting vacuum advances and "reverse" acting which is very confusing to me. I just checked mine with a vacuum gauge; the ported connection has 5 inches of vacuum at idle and as soon as you just crack the throttle it goes to manifold vacuum. The timing advances a little when connected to the ported source at idle which is telling me that the advance is working. When I connect the distributor to full manifold vacuum you can hear the advance plate slam to full advance inside the distributor, again verifying that it is working. I also verified this with a timing light. So now I know.... quit reading things on the internet! Except here of course. Thanks for the info!

[KULTULZ]

Originally Posted by Ricks56

So now I know.... quit reading things on the internet! Except here of course. Thanks for the info!

Well, there is a reason for using either, good and not so good. GM used the manifold vacuum whereas FORD did not (other then LOAD-O-MATIC) until 1968 IMCO.

The previous discussion (where I became pivot man for some reason) was not an adult discussion on the merits/problems of either but just one person saying his way was the right way and if not believed you were an a$$hole and have a nice day.

There are days like that.

[miker98038]

No WWIII, just trying to learn here. I never saw any vacuum signal at idle on ported vacuum, just when off idle. But I’ve only looked at it on 4 barrel carbs. Is there a difference, something else, carburetor adjustment needed?

[scicala]

It all depends where the siphon hole/s in the throttle bore are in relation to the throttle plate, as to how much, if any vacuum is available at idle on a carb with timed ported vacuum advance. All carbs tend to vary this dimension and hole size.


Sal

[miker98038]

Thanks, Sal.

[KULTULZ]

Originally Posted by miker98038

No WWIII

... OH MAN!

No food fights?

, just trying to learn here. I never saw any vacuum signal at idle on ported vacuum, just when off idle. But I’ve only looked at it on 4 barrel carbs. Is there a difference, something else, carburetor adjustment needed?

In addition to Sal's excellent information ...

That's why you are directed to first set to factory curb idle and remove vacuum signal.



Now if you have a modified engine with different carburetion/timing events, you are on your own.

[Kahuna]

I use full vacuum signal, not ported