My '68 Dart engine idle seems to change with the weather. I bought it
around Christmas and the idle was smooth after warm up on cold days.
As the weather has warmed the idle has gotten rougher. Today it was quite
warm and it quit several times when moving out from a stop, also the
idle is rough. Once the car is tooling down the road it's smooth and responsive. At one point I had to keep the idle high by pressing on the
gas and brake at the same time to avoid stalling.

Have you checked your spark plugs? Maybe they are starting to foul.

Replaced my plugs and wires. The old plugs were pretty clean. They were
Atlas brand?? and they were all tan to dark brown on the ends, all were
dry with no sign of oil or gas fouling.

I think I may have a vacume leak somewhere because after changing the
plugs and wires I took note of how much dry dust and dirt was on
the engine and and it's surrounds. I sprayed the engine and compartment
with a mild degreaser then started it up and hosed it down with the garden
hose (yes the engine was cold). The rough running went away for the most
part. Now I need to isolate the leak by checking the vacume lines one by one.

Some things I am confused about:
The plugs had a thin metal (aluminum?) tube around them, sometimes
they would come loose with the plug, othertimes not. The ones that I removed with the plugs had a very old and hard gasket where they met the head. Do I need to replace those gaskets? Could these hardened gaskets be causing the vacume leak?

Also, While examining the carb I found a piece of hose coming from the
top front of the carb about 3 inches long going to ....nowhere. I put my
finger over the hose but there was no change in the rough idle or any
evidence of vacume or pressure from this hose.

This is the original 1 barrel. The air cleaner says "Champion 225". The
carb is quite clean on the outside.

Thanks in advance for any advice

ballout

The spark plug tubes are not open to a vacuum source, but hardened gaskets will leak oil. It's getting harder to find the replacement seals, but NAPA carries them and they sometimes come with new spark plugs.

The hose you are referring to is probably the one that would go to a vapor canister. It won't affect your idle.

A '68 doesn't have many places for a vacuum leak, but I would check the PCV valve, the hose and the point where your PCV hose enters the base of the carb. That area will often plug up with carbon and cause a rough idle.

Spark plug tube seals never come with spark plugs—never have. Fel-Pro ES12794 (set of six plug tube seals) or NAPA Victor-Reinz B45384 (individual spark plug tube seal) is what you need.
No vapor canister on a '68. They didn't start til '72. But you're right, the line he found sounds like the '70-up ducted bowl vent line, which starting in '72 would have been connected to a vapor canister.
Between 3 and 7 vacuum hoses, depending on vehicle equipment
Between 2 and 4 places in the carburetor, depending on carb type
Carb to intake junction
Intake to head junction

That's enough places to use up an afternoon checking!

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

No, as 64 Convert writes, leaky plug tube seals won't cause a vacuum leak, but will cause an oil leak. Do replace with new. Also remember, don't use the metal ring gaskets that come with the new spark plugs. The plug tube is the gasket on '63 through '74 slant-6s.
That means somebody has installed a '70 or later carburetor on your engine. That's a ducted bowl vent hose that would have been connected to the crankcase on '70 California and '71 49-state-and-Canada models, and connected to a charcoal canister on '72-up models. It's not causing your vacuum leak.
Probably "Charger 225", which is how the engine was labelled when installed in a Dodge. ("Super 225" in a Plymouth).

Gasoline formulations do change, sometimes widely, with changing seasons. So it's normal to do some readjusting for seasonal gasoline changes. But it really sounds like heat is causing some problems all by itself. Have you checked your heat riser valve (manifold heat control valve) to make sure it's not stuck in the heat-on position? Rough hot idle and hot idle stalling are classic symptoms of a stuck-on heat riser. How about the fuel line, have you fixed it yet?

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

Those sparkplug tube seals come in the engine gasket sets too. For whatever strange reason, even the full engine sets for the hydraulic lifter engines come with those seals too. I have a extra set or two around here some place that I will never use because I do not have any pre-1975 engines or heads. I suspect many other people rebuilding S6 engines with later heads also have these seals too.

Thanks all,

It's good to know the part # for those plug tube seals!

My bad! The air cleaner does say "Charger 225".....spark plugs...air cleaner... I get confused! They do the same thing..... right?

FYI this car has "factory" AC.

By my last count I had 3 vacume take offs from the engine:
carb to distributor, carb to pvc, intake to firewall (heater AC ect.)

Thanks for solving the "mystery" vacume line.

While this car has low miles it did not have any repair records so
I have no clue as to what is original and what may have been
replaced.

Fyi, When I run the lights or heater the alt draws down to the discharge
side of the guage. Re. more electrical draw slows the idle.

Thanks in advance for any replys.

ballout