Emissions part???
 

This is located on the pass side on the intake. It has 3 wires and a vacuum source from the carb. I noticed it had a line with a screw so I put a vacuum cap on it.

What is this device? Where does the vacuum line go to? I also see what appears to be another nipple on the backside by the elect. plug.

Anybody have a 72 vacuum diagram they could share? Mine is a 350.

advance cut off
 

It is somewhat emissions related. It is a vacuum advance cutoff. It basically allows no timing advance until the motor has warmed up to operating temperature. The wiring would connect to one or two relays attached to the firewall either next to the fuse block or near the heater box. A 2nd temp. sending unit located on the passenger side of the block would trip the solenoid and open of vacuum to the distributor when it warmed up. If you look on the passenger side of teh block between the 6th and 8th cylinders, you should be able to see the sending unit or at least a plug where it once was.

Unless you're going back to stock, feel free to remove it along with the associated wiring. Your vacuum advance for the dist. should be hooked up to the carb where the vacuum solenoid is currently hooked to (ported vacuum). The wiring harness going up to the relays on the firewall and down to the sending unit is self contained and can be removed without cutting into any of the engine harness.

Hope this helps you out.

Thanks J. I would have never guessed that. PO installed an HEI and I was just about to check the ported advance and change wires as they are arcing.

TCS? Cuts off vacuum advance except in high gear.

Must be a California truck or something, my 72 was all original and it never had anything like that.

TCS. Had a 72 Blazer with that. Built and sold in Michigan.

The TCS system was not installed on the C 20 trucks and larger.

Jim

Ok, didnt think about that. Glad I don't have any of that crap to remove on my truck.

Pretty sure it is from Arkansas.