'67 AFBs, Vacuum advance connection is pretty high.I'll check my '67 FSM for that carb.
The spark port is about middle of the transfer slots, way above the idle discharge port.
Be interesting to see if other versions were different.
'67 AFBs, Vacuum advance connection is pretty high.I'll check my '67 FSM for that carb.
Maybe that's what mine is. I will look tomorrow.'67 AFBs, Vacuum advance connection is pretty high.
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The spark port is about middle of the transfer slots, way above the idle discharge port.
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Be interesting to see if other versions were different.
Ported vacuum has the vacuum inlet above the throttle plate, so with the throttle closed it sees no vacuum.In a relative nut shell...
Manifold vacuum will be high at closed throttle.
Ported will be high at open throttle.
Some older Ford's I have had had both going to the advance canister. And it kind of averaged the two.
The CAP valve does some thing with both to slow the timming return to no vacuum, IIRC. There is a CAP factory manual on imperial club web site again IIRC
Crazy you mention that but my original HP273 AFB carb only has one vacuum port for the distributor. Manifold vacuum. I should snap a picture tomorrow.
Ported vacuum has the vacuum inlet above the throttle plate, so with the throttle closed it sees no vacuum
Manifold vacuum has the vacuum inlet below the throttle plate, so with the throttle closed it sees full vacuum.
As the throttle plate opens ported and manifold vacuum are the same.
Full open throttle, ported and manifold vacuum will be near zero.
Manifold vacuum is used to add ignition advance at idle. Adding advance at idle is helpful to stabilize idle quality and prevent misfires at idle and engines that have cams with overlap that results in reversion and exhaust gases getting back into the intake charge. That exhaust and fresh charge is more difficult to light off and burns slower when lit, so on some engines and some cams, it is useful to add advance to the ignition at idle.
Off idle, as the throttle is opened ported and manifold vacuum are the exact same.
Hey Matt, I dug out my carb. You were right. Looks like ported vacuum. The nipple is quite high though. A strange looking slot though.'67 AFBs, Vacuum advance connection is pretty high.
View attachment 1715407111
The spark port is about middle of the transfer slots, way above the idle discharge port.
View attachment 1715407114
Be interesting to see if other versions were different.
Hey Matt, I dug out my carb. You were right. Looks like ported vacuum. The nipple is quite high though. A strange looking slot though.
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Yes I did!You said nipple.
i agree that the placement of the vacuum inlet has a part in ported vacuum response signal. You raised a good point.is ported vacuum really zero at WOT? I thought velocity through the venturi where the port is located would produce a vaccum, ala Holley vacuum secondary carb? Looks like this type of port is higher in the venturi (choke point) where as these ported pickups are lower....maybe the placement is key? Seems you would get tip in vacuum then it would get stronger as velocity increased past the port? I guess graph proves this wrong as throttle at 90 (WOT) produces same if not slightly lower vacuum using a standard location port right above the throttle blade.
Holley velocity sensing port placed high at choke point of smallest venturi diameter"...Vacuum for the diaphragm is supplied initially from one of the primary venturis. As rpm increase, so does velocity through the primary venturi, resulting in a progressively stronger vacuum signal..."
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Mike...I think you meant "ported" port. My 4295 ('67) AFB only has one port...ported Vac.Crazy you mention that but my original HP273 AFB carb only has one vacuum port for the distributor. Manifold vacuum. I should snap a picture tomorrow.
It's actually the same as manifold which is close to zero on a 4 bbl, but even then not zero.is ported vacuum really zero at WOT?
I think the other two guys covered this, so I'll just throw in some illustrations,I thought velocity through the venturi where the port is located would produce a vaccum, ala Holley vacuum secondary carb? Looks like this type of port is higher in the venturi (choke point) where as these ported pickups are lower....maybe the placement is key?