[mysticmissle]

Car is a 68 Firebird It has a 1/8” line coming from the front of the car I assume it gets a line to the air cleaner but I doubt it’s factory what is it?

[77 TRASHCAN]

Some of that old stuff, that pipe went to the vacuum advance...

[mysticmissle]

You think it’s factory?

[77 TRASHCAN]

My 67 Chevrolet Bel Air, 283 2G (the small one) had such a pipe.

[steve25]

Was that car from CA originally?

That location on the carb is usually where there’s a Ported vacuum nipple, so it’s kinda odd to me that there’s no nipple, but a brass adapter, but who the hell knows?

[mysticmissle]

I don’t believe it to be a cali car but don’t know
Probably won’t get the phs

[misterp266]

It looks to me as if it goes into the fuel bowl area. Seems added. Take the top off and have a look.

[shaker455]

Originally Posted by mysticmissle

Car is a 68 Firebird It has a 1/8” line coming from the front of the car I assume it gets a line to the air cleaner but I doubt it’s factory what is it?

That's spot below the bowl is generally used as a ported and full vacuum source and never seen it used to power a PCV.

That's someone own rigging.

[geeteeohguy]

Originally Posted by shaker455

That's spot below the bowl is generally used as a ported and full vacuum source and never seen it used to power a PCV.

That's someone own rigging.

I agree. Vacuum advance line that is home-made and oversized.

[mysticmissle]

Originally Posted by shaker455

That's spot below the bowl is generally used as a ported and full vacuum source and never seen it used to power a PCV.

That's someone own rigging.

Ok but Why lol thanks guys!

[Sirrotica]

FWIW, vacuum modulator source would be my guess, depends on if it's manifold vacuum, or ported. You'd need manifold vacuum for a modulator to operate properly.

As has been said, I have seen hard lines in the mid 50s engines to operate the vacuum advance, but by the late 50s, early 60s the factories had pretty much gone to hose connections. Also on truck applications I have seen hard lines used for distributor vacuum advance, with just a short piece of hose before the advance can so the distributor timing could be set.

[mysticmissle]

I guess if it probably was added when the turbo 350 was added it makes sense thanks again

[steve25]

I have factory vac line routing diagrams around somewhere, but they may only go back to 1970.

I will dig around later and post if I have them for 68.

[pfilean]

Really looks like the proper location for a ported advance. Tube was probably originally rotated to bend up then down before going toward the firewall. And if the carb was originally off a Chevy that would be the proper location for the advance diaphragm.

[Kenth]

Carb is a 7028071 used on a 1968 Pontiac 350 Firebird/Tempest M/T from factory.
In 1968 GM and others started retarding ignition timing by using a ported source for the vacuum advance to heat up the cylinder heads to reduce NOX emissions and this is what the tube in picture is used for.
Someone has twisted the tube but the end of it should point to the distributor.

[Shiny]

Originally Posted by Kenth

Carb is a 7028071 used on a 1968 Pontiac 350 Firebird/Tempest M/T from factory.
In 1968 GM and others started retarding ignition timing by using a ported source for the vacuum advance to heat up the cylinder heads to reduce NOX emissions and this is what the tube in picture is used for.
Someone has twisted the tube but the end of it should point to the distributor.

Did this go to another valve like the TCS system or was it direct to the vacuum modulator?

You note the carb is correct for M/T. Did they use the same ported vacuum on Auto cars? Just curious..

[Kenth]

Yes, but for 1968 and 1969 the valve is the T.V.S. valve next to thermostat housing.

All 1968-69 carbs uses the ported source to control vacuum advance, M/T or A/T.

[Shiny]

Thanks Kenth, that's interesting.