Do our HS6 carbs provide direct or ported vacuum?

[edgyWedgy]

Hi all,

I just read about ported and direct vacuum to use as source for ignition advance.
There's a nice little nozzle at the carb that is used on cylinder 3&4, to connect to the vacuum cannister of the distributor.
I was wondering if this always give the full manifold vacuum, or if it is some sort of ported vacuum. I cannot see where the it takes the vacuum from. My bet would be on the first, but i'm not entirely sure. Someone who knows about this?

EDIT: I disconnected the tube from the vacuum advance while watching the ignition timing; it didn't retard.
Hence i concluded that either it's ported vacuum, or my vacuum system is clogged or something.
I did hear the tube hissing, there just was barely any vacuum. Anyone who can confirm me?

Thanks and cheers.

[Beans]

Vacuum pick off on the HS is direct from the inlet flow,
just behind (down stream) and on top of the throttle disc of the carburettor.

With engine running and clean vacuum tube connected to advance unit only,
see what happens when you suck on the tube. If the timing advance increases the vacuum unit is still OK-ish.

[Hasbeen]

The 8, & 4 of the 5 7s I've owned had split distributer diaphragms when I bought them.

3 of the brake booster hoses had a leak of some extent.

Not much point trying to tune an engine before fixing these little faults. The things can still go OK at higher revs, but you can never get a good idle.

Hasbeen

[edgyWedgy]

@Beans: The vacuum unit is in perfect condition. At first I thought that that thing was the problem, by having a leak in the membrane.
That'd create an air leak and a lack of ignition advance. The symptoms are similar to those of an air leak, so i bought a new one, but nothing changed. The tube that connects to it does hiss, so that indicates there is airflow. I grabbed a propane torch and put the tube in front of the unlit torch, and the engine speed fairly increased. So that indicates there's no blockage either.

If it was ported vacuum, it'd be no wonder that there's no vacuum advance at idle. If it's direct like you say, there should definitely be vacuum advance at idle. I set the static ignition advance to 10deg, but no additional advance occurs when i either or not connect the tube to the vacuum unit. I don't think i can provide sufficient vacuum with my mouth to make the vacuum unit do anything, but i'll try.

@Hasbeen
That's what i was thinking too, that the vacuum unit was the root of the problems. But it's not.(explained above)
The entire brakebooster is only half a year old, and the tube to it also. only the valve is reused. I don't suspect an air leak there. I didn't suspect an air leak at all first, because it has run really great for the last 6 months. It's only the last weeks that the performance has seriously dropped.
The symptoms suggest an air leak, but it'd surprise me if that just develops after some driving. (8000km now since revision)
It really sucks to remove the inlet manifold and carbs, so i hope it's something else...

[Beans]

Also check that the mounting plate (for the points) inside the dizzy moves freely. I have seen one that was rock solid.
It was caused by a PO who had used an incorrect screw to fit the points, thus locking both parts of the mounting plate together.

[edgyWedgy]

Good point, it indeed moves freely. Ie. i can rotate it by hand, only feeling the spring in the vacuum unit holding it back.