Vacuum line from air cleaner

[Boonie]

So, I have looked for this on the internet, and I'm either not finding it, or I'm not recognizing it when I do find it, but I need to know where the vacuum line from the air cleaner connects to on the carburetor. Its on the underside of the snorkel, and goes to one of the ports on the carb. I just put a new SMI quadrajet on it, runs great. I don't know how important this line is, or if it is at all, but I don't like having stuff just hanging or tucked away somewhere in the engine compartment. Thanks again for all your help

 

[MadOgre]

83' k20

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[chengny]

That is the actuating line for the Thermac system's vacuum motor. It is designed to bring in warm air (from off the RH manifold via that flexible hose) while the engine is cold.

There is a temp sensor in the air cleaner housing that controls the valve. When the sensor sees air at about 90 F, it tells the vacuum motor (and the valve attached to it) to close off the flow of hot air from the manifold and begin drawing in cool air through the normal opening in the front of the snorkel.

I would not worry about even hooking it back up. It was an early device developed by GM to satisfy some EPA requirement.

First of all, a Chevy 350 will run just fine on cold air (no preheating is required).

Secondly, probably the biggest reason for eliminating the vacuum tubing is that the Thermac system on your truck probably hasn't worked in 20 years.

 

[Georgeb]

That is the actuating line for the Thermac system's vacuum motor. It is designed to bring in warm air (from off the RH manifold via that flexible hose) while the engine is cold.

There is a temp sensor in the air cleaner housing that controls the valve. When the sensor sees air at about 90 F, it tells the vacuum motor (and the valve attached to it) to close off the flow of hot air from the manifold and begin drawing in cool air through the normal opening in the front of the snorkel.

I would not worry about even hooking it back up. It was an early device developed by GM to satisfy some EPA requirement.

First of all, a Chevy 350 will run just fine on cold air (no preheating is required).

Secondly, probably the biggest reason for eliminating the vacuum tubing is that the Thermac system on your truck probably hasn't worked in 20 years.

Right on^^
I haven't seen a working one yet. Not important.

 

[Boonie]

I would guess it hasn't worked in longer than that. just trying to get it back to what it was when granddad brought it home. lots of memories with that truck, kinda building it in his memory

 

[rich weyand]

I disagree that it is not important. See this post in another forum.

http://www.fullsizechevy.com/forum/...m/498719-induction-system-350cid-headers.html

 

[MadOgre]

I disagree that it is not important. See this post in another forum.

http://www.fullsizechevy.com/forum/...m/498719-induction-system-350cid-headers.html

I disagree with your disagreement lol!

As you know I use a winter front come cold weather. My truck actually runs better when the winter months come with better mpg. I even use the restrictor plates for the cross over. The Eddy's electric choke works well enough that I can set it to stay on long enough to keep the engine happy till its warm enough to do so by itself, at -30* Celsius. With a winter front! mind you. It wouldn't work to well with out a winter front. I put the winter front on at -5* Celsius and cooler. I simply rely on under hood temps to warm the incoming air to the carb. I also think that the PCV system for the round open air cleaners aids a little bit in producing warm air to the carb.

If however I was to use the snorkel with out the Thermostatic valve I would likely have issues with stalling and sputtering. But with the open element, it allows all the heat from the entire engine to be sucked into the carb, as we all know heat rises, and it rises right into the round open air cleaner. Aided by the fact that I use the winter front.

Honestly with my set up there is no difference between summer and winter months for me except that it takes a bit longer for the engine to warm up at -30* But even our new FI vehicles don't like the super cold weather all that much either.

Also I have knocked out both knock outs to aid in summer driving. This is a non issue in the winter because I use the winter front.