Hard vacuum line to the carb - questions.
 

I’m curious about the hard vacuum advance line. All motors? All models? Different styles for different years? What about AIR equipped motors? Affixed with spring clamps at the rubber hose?

Can anyone shed details?

Neither of my SB motors have these so looking to add if original equipment. A BB motor I used to own did have this line.

Borrowed example pics show the line joining the carb on the LH front port.

Re: Hard vacuum line to the carb - questions.
 

Vacuum likes generally just have a bubble flare since the outside air tends to compress the hose a tiny bit, so no clamps. I've only ever seen clamps on the brake booster hose but I expect that that's because the engine moving could eventually work it loose. The vapor canister lines also had clamps, now that I think about it. At least the one to the carburetor vent.

Re: Hard vacuum line to the carb - questions.
 

My 71 K1500 with v8 350 had the hard line from the Distributor to the CEC valve. I'm not sure what years used the CEC valve that turned the vacuum on or off based on several different engine/transmission conditions. When I acquired my truck the hard line was present, but the CEC valve was bypassed. I've never really figured out the correct routing as every way I've tried doesn't seem right. I would like to see any photos out there that show the factory routing.

Re: Hard vacuum line to the carb - questions.
 

In my photo in post #3, the hard vacuum line looks kind of correct. I big chunk of the line ran down the valve cover rail, which would make sense. What throws me is when I try to route it to the CEC valve and not directly to the carb.

Re: Hard vacuum line to the carb - questions.
 

My truck is in paint prison so I can't take a look right now. Best as I can recall, the hard line looks like the second pic in post #1. Short rubber hose on each end, no clamps, and I'm pretty sure it's original to my California K20.

Re: Hard vacuum line to the carb - questions.
 

Thanks for posting. FWIW Inline Tube lists a repro in their catalog for 71-72 (steel and stainless). I’ve ordered one to try and I’ll post a review. With IT though you never know 1) if it will fit or 2) if they send what you ordered :)

https://www.inlinetube.com/products/ctv7103

Re: Hard vacuum line to the carb - questions.
 

The 1/2 tons in 71-72 had the solenoid for the TCS mounted along the RH head. I’ll dig for a schematic as I’m curious how it ties into this hard line if at all.

Edit: Maybe the line serves to supply the manifold vacuum port on the vacuum advance solenoid for the TCS set up? For 3/4t pickups that weren’t equipped with TCS maybe the rubber hose was just a tad longer going right to the distributor from the rear of the hard line?

Re: Hard vacuum line to the carb - questions.
 

Here’s an example also form the service manual albeit a Mark IV engine

Re: Hard vacuum line to the carb - questions.
 

Here are pictures of what's original to my '69 C20 with a 350 and no emissions other than a PCV. They show rubber at the ends and steel in between and no clamps. I believe the original rubber line to the vacuum advance was a bit shorter.I transferred the clip in the last picture from the original engine to my crate engine. It was attached to the hard line and the intake.

Re: Hard vacuum line to the carb - questions.
 

Jim thanks for posting. Now I need to locate two of those tiny clips.

The Inline Tube piece looks like a decent match and it seemed to fit well. Arrived inside a bubble pack. I’d recommend it. They offer a stainless version also.

Re: Hard vacuum line to the carb - questions.
 

Like this? Looks right to me.

https://www.corvettecentral.com/c3-6...cuum%2badvance

Re: Hard vacuum line to the carb - questions.
 

I also found these valve cover clips for the temp sender wire. They look very familiar, but it looks like my '58 Vette has them. However, they'd work well with aluminum valve covers and possibly steel on these trucks.

https://www.corvettecentral.com/c3-6...n-valve-302055

Sorry for the subject change...

EDIT: After checking further, I think my original valve covers had/have clips welded on to the left valve cover. I'll have to check.

Re: Hard vacuum line to the carb - questions.
 

A 72 K20 that I restored only had one clip holding the steel line and no clamps. My 70 K20 that I'm working on now has the same single clip and a similar steel line.

Before and after restoration pics of the 72 K20 -

Miles

Re: Hard vacuum line to the carb - questions.
 

Very helpful thanks guys. I ordered a pair of the clips.

Re: Hard vacuum line to the carb - questions.
 

Only one on mine also.

Re: Hard vacuum line to the carb - questions.
 

Thanks - I've ordered one for each motor that needs it