Zenith carb - connections

Deesta

Member
Messages
59
Reaction score
2
Location
Brisbane
Ok. I had the zenith carbs completely rebuilt. I have installed them and hooked up the lines to the fuel pump but for the life of me can't figure out the other connections. I have searched the web and can't find anything. Does anyone have photos of their setup. Thanks.
 

deQuincey

Well-Known Member
Site Donor
Messages
6,154
Reaction score
695
Location
bilbao
Ok. I had the zenith carbs completely rebuilt. I have installed them and hooked up the lines to the fuel pump but for the life of me can't figure out the other connections. I have searched the web and can't find anything. Does anyone have photos of their setup. Thanks.
it is nice to know where are you from and some details about the car, being a coupe, there are several versions

then, it will help if you post some pics of your carbs to know which type of carbs they are, i have found more than 4 types of zeniths in my life, so it will probably help to know what you have laying down there
 

Stevehose

Well-Known Member
Site Donor $
Messages
9,483
Reaction score
1,643
Location
New Orleans, LA
What year is your car? Do you have emissions stuff still in use? Does your distributor use the advance and retard lines? Take some pics of the engine compartment with the air cleaner assembly off.
 

Deesta

Member
Messages
59
Reaction score
2
Location
Brisbane
Photos attached.

Good advice. I should have realised there were different versions. It's a 1974 3.0cs. Photos attached. Appreciate any advice.
 

Attachments

Last edited:

61porsche

Active Member
Messages
1,733
Reaction score
20
Location
Dallas
Here's a

start:

Chokes are water and electric.

The electric starts from the rear carb, green wire, small wiring harness on the other tab to the cold start enhancement ( silver aluminum cover box on the booster side) to the fuel start solenoid loops to the front carb same sequence. ( won't idle til you do this.)

Water should be evident. Back of block to one side of rear choke, hose to front carb, other side of front choke to near front of block. ( A loop).

Not related, but need to hook up your oil pressure sw

Vacuum- front carb, side near valve cover, near bast. Connect to vacuum can on distributer. Plug/ cap all the rest. There are several.Both sides and manifolds.
 

Deesta

Member
Messages
59
Reaction score
2
Location
Brisbane
Carb update

Firstly thanks 61porsche for your response way back in May last year. I have been busy restoring the rest of the car and now have come back to the carbs. Anyway more advice required. Attached are two photos. One is a rough picture of the carbs and the connections. There other is the harness I have.

Now there are 4 connections on each carb:

1. Cold start enhancement
2. Solenoid
3 and 4 are on the automatic choke

Actually the front carb should has the temp sensitive switch however when they were rebuilt the carb they used the wrong bottom plate and as such it's not there. I live I a warm climate so hoping that I don't need it. If I do please let me know as I have the correct bottom plate with the switch in it (want to avoid having to pull the carb out to fit it).

I have labelled the relay and wires. If someone could please let me know which ones go where. I do know that 85 is supposed to go to the temp sensitive switch but as mentioned hoping I don't need it.

I have also attached a picture of my wiring harness. Is someone could tell me if I need all the connections.

I have spent a full day trying to figure it out!! Anyway thanks in advance.
 

Attachments

bavbob

Well-Known Member
Site Donor
Messages
1,233
Reaction score
169
Location
Boston, Ma
DeQ I think will agree....run a vacuum hose from one carb base to the other, it just adds a little smoothness to the final product.
 

Peter Coomaraswamy

Well-Known Member
Site Donor $
Messages
3,507
Reaction score
616
Location
Austin, TX
This will not help

So I thought I would try to help and take some shots of my Zeniths as they are all connected now, but maybe not. Anyhow, the wires are hooked up but nothing seems to be hooked up to them, meaning the sensors or whatever all have wires but none are hooked up to the harness so I took a final picture of the "free" wires coming out of the harness (picture 3) and maybe if someone can tell us where they go then we'll have a complete picture?? :-(
 

Attachments

61porsche

Active Member
Messages
1,733
Reaction score
20
Location
Dallas
Temperature

switch(s) in the intakes manifolds are not needed and were not used on all cars. They were used as an idle emission device with a lot of other emission items.

85 is not used.

But that wire black/ brown is a mystery wire that several other recent posts describe and you found.

A simple explanation to your other question- the green wire (hot switched) powers all the chokes, idle solenoid valve, and the cold start enrichment; in series- all tied together. That's how the early cars are wired.

Yes, tying in the vacuum from each manifold improves idle ( slightly) by smoothing out the intake pulses seen by the carbs and distributer. The original SS lines that fed the emissions controls had another purpose. I picked it up while studying Rolls Royce/ BMW engines used in fighter planes. I tried it and it worked for me. Not a huge difference, but noticeable.

DQ's got an oscilloscope tester- DQ- did you ever go through the whole BMW test program? :cool:
 

61porsche

Active Member
Messages
1,733
Reaction score
20
Location
Dallas
Front

carb has no power. Green/ white. I can't see the top of the chokes. Early carbs were fed from the rear carb choke and the other side loops all the other devices.

You need one switched ( green) power feed run in series with all carb devices for it to run. It's fed from the fuse box or through the relay in discussion.

Test the two green/ white wires.
 

Deesta

Member
Messages
59
Reaction score
2
Location
Brisbane
Resolved!

Well I finally got it all hooked up and thanks for your advice. Funny enough there were not wires that went to the cold start enhancements on either carb. Could this because its an Australian delivered (it doesn't really get cold here, well not in Brisbane).

I have attached an updated diagram (albeit a bit rough).
 

Attachments

Deesta

Member
Messages
59
Reaction score
2
Location
Brisbane
Vacuum connections

Hi. Thanks for your advice on the carbs. There seems to be varying advice on the Vacuum connections. I have attached a diagram of my setup and hope you can tell me what to connect to where. Thanks again.
 

Attachments

61porsche

Active Member
Messages
1,733
Reaction score
20
Location
Dallas
Conventional

wisdom based on the practicality that the emission devices are no longer on your car is:

1. Distributer advance- from front carb, port closest to valve cover. Distributer retard is not used.

2. The rest are all capped to include the egr ports on the manifold. Check this to make sure they are tight since various methods have been used- a real metal cap, crimped and soldered egr tubing, etc. I've found leaks there.

3. Optional- tie the carbs together. Simple- the two ports closest to the fender. This assumes you've tuned each carb by a vacuum guage. The theory is that multiple carb installs benefit from a steady ( constant) source or that manifold pulses are optimized, or if one bank of cylinders is slightly different it balances out the equation. Works for some, not for others.

4. I didn't try this, but will next time I do a major tune- the two manifolds tied together if T'd might improve the vac signal to the distributer.

Here's the original EGR/ VAC setup for most as there were several including a CA only version w/ air pump and fuel return line:
 

Deesta

Member
Messages
59
Reaction score
2
Location
Brisbane
Vacuum connection confirmation

Thanks 61porsche for your advice. Following is a photo of how I connected the vacuum hoses as per you advice. Have I got it right?
 

Attachments

deQuincey

Well-Known Member
Site Donor
Messages
6,154
Reaction score
695
Location
bilbao
Thanks 61porsche for your advice. Following is a photo of how I connected the vacuum hoses as per you advice. Have I got it right?
as far as i can tell
if you have the stock air filter, then the red hose beteen front and rear carbs should have a "T" in the middle and be connected to the tiny tube on the air filter
 
Top