Qjet to Edelbrock 1400 vacuum line puzzle- I need help

[77Matt]

1977 GMC C1500 Heavy Duty 350 V8 failed smog due to extremely high HCs

I am swapping out the the 4MV Qjet for the Edelbrock 1400 and need help with th vacuum lines. Pic 1 is what the set up should look like. Pic 2 is the current setup with the Qjet. The PCV and canister have dedicate connections to the carb. There are two remaining ports available on the Edelbrock, 1 manifold and 1 times/ported. If I keep the current configuration, what goes where? I color coated and numbered the vacuum lines I’m unsure of. Number one goal is to pass smog test. I will address power and fuel efficiency once smog is taken care of. I’m adding a 3rd pic of what I believe is the ‘spark control switch’ (red arrow) and ‘control valve’ (blue arrow) in case I am wrong (maybe it’s EFE?). What is the best configuration to pass smog? Note- heavy duty did not have EGR systems or Cats. If it doesn’t smog after this, I will take the advice in a different thread and put on a couple cats (dual exhaust) - the truck needs headers anyways. Thanks in advance

 

[Radiohead]

I need to crash tonight, but I am going to check back later and see how it goes.

 

[75gmck25]

It looks like your Quadrajet must be set up like my original ‘75 carburetor, where there is a dedicated port for the vacuum canister. When I swapped to a 1980+ Quadrajet it did not have that port.

I have not been able to find an original vacuum diagram for my ‘75 350 with HD emissions. I’ve also never figured out exactly how the original vent control for the canister works, since there is no separate purge valve. I’m also not sure if it’s function might be related to your high HC levels.

I T’d into the PCV line and connected the canister vent there. It seems to work, but probably creates a vacuum leak at idle. However, I can still get the idle mixture set without any issue.

If you have an actual 1400 Edelbrock, it is probably fairly rich out of the box. If you look at the specs for the 1406, which is their “economy” version of the 1400 series, you may want to try its primary jets and rods. However, I don’t really understand the emissions data, so maybe I’m heading you in the wrong direction.

 

[82sbshortbed]

I'm so glad I don't have to deal with this bs. Being I'm in Texas, I don't have any smog crap on either one of my squares. Gotta love California. Hope you get it to pass. You can also use manifold vacume for some of those vacuum hoses.

 

[fast 99]

For emissions diagnosis providing all the failure specs would help. Saying high HC there are degrees of high. As I posted in another thread high HC is generally anything other than fuel. If CO is low could be a lean condition. Normal CO would tilt toward other issues or a combination.

Assume a near stock cam. HP cams are not emissions friendly.

Things to check, over advanced, lean, vacuum leaks, misfire, flat cam, general engine wear. Others may have additional suggestions.

 

[77Matt]

For emissions diagnosis providing all the failure specs would help. Saying high HC there are degrees of high. As I posted in another thread high HC is generally anything other than fuel. If CO is low could be a lean condition. Normal CO would tilt toward other issues or a combination.

Assume a near stock cam. HP cams are not emissions friendly.

Things to check, over advanced, lean, vacuum leaks, misfire, flat cam, general engine wear. Others may have additional suggestions.

Here is the sheet. Circled is measured and Max is the expectation. CO an NO err fine but HC was sky high. The smog guy also disconnected the PCV hose on the side that feeds into the air cleaner. I didnt notice until I got home. I’m sure that had an affect but didn’t think that big of an affect. I have to fix a fuel leak also, hence the new carb. Now I want to get the vacuum lines hooked up correctly to see where I stand. Thanks

 

[77Matt]

I believe the blue to green line in the original diagram I posted above - the vacuum circuit that goes through the control valve, has a function in the choke. Since the Edelbrock has an electric choke, I dont think I need this. Is that correct?

 

[77Matt]

Vacuum lines actually weren’t that complicated. The ‘control valve’ was required for the quadrant function but not for the Edelbrock. Yellow line went in to manifold and purple into ported/timed. Seems good. Few hiccups along the way but testing tomorrow.

 

[ButchM]

Matt, does your rig have air conditioning?

 

[77Matt]

Yes it does.

 

[ButchM]

Yes it does.

Fig CL31 is for CA HD emissions with A/C. I believe the figure you had was CL 30 for non A/C trucks. It appears the diff is the addition of a spark control switch. I hope this helps.

You must be registered for see images attach

 

[ButchM]

http://www.73-87chevytrucks.com/techinfo/7387CKMans//Service/ST_330_77_1977_Chevrolet_Light_Truck_Service_Manual.pdf

Throttle Control & CA Emissions

Throttle Control & CA Emissions

forum.73-87chevytrucks.com

 

[ButchM]

I hope one of those will get you to the link for the manual and it will help.

 

[77Matt]

Quick update - Passed CA SMOG by capping the 'EGR' port on the EB 1400 and teeing manifold vacuum from the brake booster to feed the ported vacuum switch (labeled spark control valve in the diagram i posted earlier). She's on the road again and sounds great.