1972 C10 350 Quadrajet Engine Vacuum Lines

[BamaC10's]

Hello and good afternoon. I've got a 1972 C10 with 350 and Rochester Quadrajet. I've looked but can't find my set up for the engine vacuum lines. I'm guessing most of the original stuff gets bypassed but I'm trying to restore one. I'm not 100% sure what this is called or it's function but I need to know how to plumb it out. I'm calling it the vacuum switch. Your help is appreciated!

[68 P.O.S.]

That's part of the old transmission controlled spark (TCS) system. It was an early, crude attempt at emissions control. You can get rid of it; it does your engine no favors. Do a quick search for it, there's lots of info here on it.

[BamaC10's]

Originally Posted by 68 P.O.S.

That's part of the old transmission controlled spark (TCS) system. It was an early, crude attempt at emissions control. You can get rid of it; it does your engine no favors. Do a quick search for it, there's lots of info here on it.

Thanks! Knowing what it's called helps.

[towbar]

Doing the same thing that BamaC10's is doing, mine has the same switch set up, if its better to delete it, then that's doable, but would still like to see the schematic of vacuum lines....have searched the web and not come up with I need for carb and charcoal lines etc.

[Steeveedee]

The ported spark port used for the TCS was at the 1/4" (I think) tube on the driver's side in the front of the carb. The hose went to the switch and then the distributor. If you want to continue to run ported spark (vacuum only when the throttle is a bit off idle) simply run a hose from the carb to the distributor. There will be a switch on the transmission that closed when in high gear. If you see what looks like a switch for oil pressure with a light, that's it. Unless it's leaking, just leave it alone. Some applications went through a thermal vacuum switch mounted (usually) into the thermostat housing. The idea was to reduce emissions of oxides of nitrogen by delaying vacuum advance until the engine was up to operating temperature and in high gear.

[towbar]

That's some good info Steeveedee! thanks
Any idea on where the vacuum lines from the charcoal canister fit into the mix? I think the large one 3/8, goes to the vapor return on the frame to the tank, but there are two 1/4" lines I'm unsure of.

[geezer#99]

Some good info on tcs here.



http://garage.grumpysperformance.com...72-vette.9912/

[geezer#99]

Originally Posted by towbar

That's some good info Steeveedee! thanks
Any idea on where the vacuum lines from the charcoal canister fit into the mix? I think the large one 3/8, goes to the vapor return on the frame to the tank, but there are two 1/4" lines I'm unsure of.

I see you have several trucks.
What year are you looking for?

[BamaC10's]

If I decide to bypass it and run my vacuum advance straight to carb, would I need to adjust my timing? Because I did this and now I have an high idle with a little snap and pop occasionally.

BTW thanks for the replies, good information already!

[Steeveedee]

If you connected the vacuum line from the carb at the port low and in front on the driver's side directly to the vacuum advance, there should be no change. Make sure that the vacuum line isn't interfering with the choke. When those lines are run direct, there is usually a steel tube that is attached via its bracket to a manifold bolt, and there will be two shorter hoses. That keeps the hose from getting cooked on the manifold crossover port, and away from the choke.

IIRC, one of the ports on the vapor canister got to engine vacuum, one to the vapor line from the tank. The 3/8" fitting is connected to the PCV system using a "T", or more probably a "Y" fitting.

[towbar]

Originally Posted by geezer#99

I see you have several trucks.
What year are you looking for?

thanks geezer#99, same as SteeveeDee, a 72 model that I'm working on.

[geezer#99]

Originally Posted by towbar

thanks geezer#99, same as SteeveeDee, a 72 model that I'm working on.

This might help.



http://67-72chevytrucks.com/vboard/s...d.php?t=592847

[BamaC10's]

Thanks guys, turns out my vacuum advance was bad causing the high idle. I also found geezer's last link extremely helpful for vacuum routing on engine side! thank you!