Vacuum Line Frustration
 

So, I have done lots of hunting on Google, and scoured the Service Manual and I'm about ready to pull out my hair trying to untangle the mess a former owner left for me. I don't see any examples of a 4 port charcoal canister on a truck without EGR, and other than in the service manual, I dont see any examples of a second PCV ran to an air cleaner riser like mine. But the PCV lines are the only ones the manual references.

My truck is a 1971 C/20, 350, Quadrajet, no AC, no cruise, should be simple, right? I'm mostly sure the PCV lines, as well as the two lines that are currently connected to the charcoal canister (to PCV and Tank) are correct. I think the distributor is also correct (D1 to V1). I'm also guessing the small canister port goes to the timed vacuum port (C2 to V3). Where should the large canister port closest to the fender (C1), and air cleaner port be routed to? Also, what gets connected to V2, and is it to the fuel bowl?

I will attach a quick diagram, as well as a few images of what I am dealing with.

https://i.imgur.com/GCBbtrl.jpg?1
https://i.imgur.com/xrfT6bN.jpg?1
https://i.imgur.com/wsOJpyS.jpg?1

Re: Vacuum Line Frustration
 

My k20 doesn't have a charcoal canister. I didn't think any of the 3/4 tons did.

Re: Vacuum Line Frustration
 

The line from the riser to the valve cover is just an air supply breather. You need air supplied to your motor to mix with the fumes and moisture that are pulled out of the motor with the pcv.
Your other mess of hoses basically hooks up your manifold vacuum port (v2) to the ported vacuum port (v3).
Your distributor vac pot shouldn’t hook to v1. That’s a manifold vac port that should hook to the small barb on the canister.
Not sure on the rest of the stuff on the canister.
Does your air cleaner snout have a opening for a choke stove pipe?

Re: Vacuum Line Frustration
 

Mine was built in Fremont, I'm sure I can blame California. I don't see any evidence of EGR being equipped so at least I'm lucky there.

Re: Vacuum Line Frustration
 

See this is where I keep getting confused, I keep finding different opinions. I found a Corvette forum where someone recommended connecting vac. advance and the canister control valve (C2) to V3, capping V2, and connecting the air cleaner to V1.

My air cleaner does indeed have a stove pipe and a vacuum diaphragm, choke is divorced on the intake. Why would I want to connect manifold vacuum (V2) to ported vacuum (V3)?

Re: Vacuum Line Frustration
 

I don't recall seeing vapor recovery canisters on 3/4T and larger trucks in '71, and for certain they didn't have EGR. So there has been some swapping around going on. Has the cab on your truck been transplanted from a different vehicle? If so, and it was more recent manufacture than '71, it could have the vapor separator lines in the cab. It'll be obvious from looking at the tank, as there will be multiple lines to it, not just the fuel pump suction line. What does the SPID say about California emissions equipment?

Re: Vacuum Line Frustration
 

Air cleaner might have the stove pipe fitting but do you have the pipe and stove on the manifold?
Youdon’t Want manifold to ported. Seems po did though.
I’ve seen v1 hooked to the canister normally.
As to where to hook your vac advance is debatable. You could have a 10 page thread with everybody’s opinion.

What’s your ultimate goal?
Concourse restoration or just what’s needed Hooked up?

Re: Vacuum Line Frustration
 

I've seen that 10 page debate trying to figure this out, believe me. I'm just aiming to get rid of the spaghetti mess the PO left for me and get it running. Figure while I'm getting rid of rotten fuel lines I might as well replace whatever rubber may become an issue. The pipe and stove, surprisingly, are still where they belong. Come winter where would you recommend hooking the air cleaner vacuum line up to, V2? I'll go with vac. advance to ported, and canister to manifold for now like you so kindly have recommended.

Re: Vacuum Line Frustration
 

Definitely no EGR on mine, but rare as it may be it's all stock, cab and frame VIN's match, going by paint evidence not so much as a screw has been turned on the vapor recovery equipment in the cab, vapor return line, separator hoop up into the pillar and all. I am wondering if the charcoal canister may have been swapped for a newer one at some point but the rest is as it was built. I've also found the exact setup referenced in the 1971 Chassis Service Manual, it sadly doesn't include a vac system diagram. Its a CE241Z truck, no California emissions mentioned on the SPID, just built at Fremont going by the Z in the VIN, likely sold here in CO new.

Re: Vacuum Line Frustration
 

Aircleaner vac line hooks to manifold vac thru the temp switch in the aircleaner.

Re: Vacuum Line Frustration
 

Is that a CA emissions carb? Code on the LH side could let us know. Looks like has the extra port out front but don't have access to mine to compare at the moment. If so, just cap that one. The side port can go to the air cleaner. Those tee fittings are for use with the CA system and/or AC vac hoses I suspect. The larger diameter hose at the base would use a tee fitting and I think one end would send hose to the charcoal can.

Re: Vacuum Line Frustration
 

OK. The California emissions designs also correspond to high altitude requirements in Colorado. I thought that the emissions recovery system was a 1/2T only deal in those days, though.

Re: Vacuum Line Frustration
 

With all the horrible splices and wire nuts I've found in the electrical system, I wouldn't doubt the PO actually spent money on Ts to do things wrong. I know the T between PCV, carb, and canister is likely original, the rest I dont know. They got creative and cobbled a vacuum canister out of an old brake fluid can and Td it between the master cylinder and manifold as well :dohh:.

The carb is part no. 7041208 DN ?380. So using a magic decoder ring, 70-75 model, for a 71, Fed. standard 4bbl, for a Chevy, automatic?, built the ?38th day of 70. From my reading, the manual vs. auto marking can be dependent, and Fremont was notorious for doing things wrong, hence why it builds Teslas now.

Re: Vacuum Line Frustration
 

Been awhile since I've done smog checks, but let me give it a run

V1 to A1---maybe another sensor under the air cleaner
C1 stays open unless it is labeled
V3 to D1 teed to C2
Plug V2
PCV Teed to caniister

Re: Vacuum Line Frustration
 

Take it all off and throw it in the trash , You'll feel like your on vacation .:lol:

Re: Vacuum Line Frustration
 

Thanks for all the sagely advice gentleman! Between geezer and kwmech I think I should be able to stop removing hair the hard way. Ill try it both ways and see which works best, and maybe I will draw up a less cheesy diagram for the next guy who may need it.

I will say, Grumpy has the simplest answer. But I like to put things back to stock before I start modding, easier to tell if I'm the bumbling idiot that way.

Re: Vacuum Line Frustration
 

If there are no smog checks required for this year in CO then I would delete all of this also. Evap is nice in the summer though to help keep the odor out of the cab.

Re: Vacuum Line Frustration
 

LOL! You beat me to it Grumpy! Heres some diagrams from autozone, https://www.autozone.com/repairinfo/...00c152801db29f Not to throw havoc into chaos but some 71's had the TCS systems which incorporated a vacuum control solenoid that controlled the spark advance dashpot. My recommendation is, unless your doing a factory restoration, scrap all that crap and enjoy a happier motor with improved mileage. The few factory plumbed 71 trucks with stink canisters ran their distributors off ported vacuum. Many hot rodders and tuners trashed that idea for manifold vacuum. Bottom line is, you give up mileage for power at idle and cruise speeds. Your factory distributor is factory curved for ported vacuum. I don't mind the slight odor of gasoline otherwise I'd drive a new Chevy instead of a cool old truck that spanks an occasional Vortec truck, that needs a tune...;)

Re: Vacuum Line Frustration
 

Block the extra vacuum ports on the carb and just run PCV and vacuum advance.
If that canister is damaged, you will end up adding a vacuum leak.

Re: Vacuum Line Frustration
 

Fixing that old canister is going to be a 2-400 dollar pita. Its all the little crap you have to buy.

Drop kick that EPA thing back to 1967, it wont work there either.

Re: Vacuum Line Frustration
 

:gi::gi::gi::gi:

Re: Vacuum Line Frustration
 

You guys have talked me into just that. About to go buy some fuel line and vacuum line, as well as some other tune up stuff as we speak. I'm thinking I may use the vapor hard line back to the tank as a fuel return line with an AMC style vapor return fuel filter to help fight vapor-lock, but the canister is already out of the mix.