1973 Datsun 240z S30 Manual Comparison Trouble

[Thenervemann]

Hi,

So let me start off by saying I tested the compression and the adjusted the valves, cleaned the carburettors and got the car running fairly nicely. However I am getting little to no power at 3000 rpm+

My guess is that I have the timing set incorrectly and that the vacuum advance (which I had connected when setting the timing) is retarding the timing at idle giving me a false reading. Is this true? I have to go work on it this weekend. I noticed the timing advance goes up by almost 35* + when rpms increase in neutral.

Second.

I am not, for the life of me able to figure out how this manual downloaded at XenonS30 matches up with my car. The mixture screw is in a different location, the idle adjustment screws are different. I don't think I have the EGR control valve? or atleast dont have the valve in the same location.

Here is a picture of the cars engine:

I am just having the darndest time adjusting the carbs according to this manual with the different terms they use/different locations. Any help is appreciated. I have been working on this for awhile and have come pretty far from having a car that hasn't started for awhile.

Also I was wondering if there was a good stock setting for the mixture screws or do I have to adjust those according to how high the float bowl is before it shuts off according to this source: Technical Information Page ..... Carburation

-Eric

P.S. Why do I have the domed carbs when the 73's came with the flat top ones that people hated and called "boat anchors"?

Lastly, what does the round vacuum device just above the front carb do?

Edited June 24, 2014 by Thenervemann

[Captain Obvious]

The reason the manuals don't match your car is that someone has already converted your car from the original flat top carbs to one of the earlier years with the round tops.

You'll need to use the earlier manual for the carbs and the 73 for everything else.

As for the round thing near the carb... Can you be a little more descriptive? What direction is "in front"?

[Mark Maras]

The round vacuum devise is the dashpot (old term). When backing off the throttle, it momentarily prevents the throttle linkage from closing all the way to idle, A lot of Z owners just remove it. Non essential.

You have the domed carbs because a PO did you a favor. The FSM for 1970,1971 should be the one to use but ZTherapy's SU DVD contains ALL the info you will need to fully understand the carbs. Believe me, SUS are not complex at all.

[Thenervemann]

For lack of better words: its the round metal canister thing that is above the carb on the left side of the photo.

[Thenervemann]

The round vacuum devise is the dashpot (old term). When backing off the throttle, it momentarily prevents the throttle linkage from closing all the way to idle, A lot of Z owners just remove it. Non essential.

You have the domed carbs because a PO did you a favor. The FSM for 1970,1971 should be the one to use but ZTherapy's SU DVD contains ALL the info you will need to fully understand the carbs. Believe me, SUS are not complex at all.

I believe that device you are referring to is the device that interacts with the linkage, and connects to the throttle control valve opener. I am talking about the device that is directly above the front SU carb. This device, I believe is not connected to the throttle linkage in any way. it looks like its connected to the manifold. (highlighted in red in this photo):

[Captain Obvious]

The device inside the red box is called your anti-backfire valve. It has three ports:

Clean air IN from the air cleaner by way of the air pump. That's the largish hose on the left.

Clear air OUT to the manifold when called for. That's the largish hose on the right.

Control vacuum line, That's the small line that goes to the balance tube.

The device's function is that when manifold vacuum gets very high (as sensed by the control line on the balance tube) the valve will open and allow air to pass through the valve into the balance tube.

It's function is to dilute an overly rich mixture that occurs under high RPM deceleration conditions.

See manual EC (emissions control) section.

[Thenervemann]

thank you very much.

[Thenervemann]

does anyone know what the timing should be after it advances at higher rpm?

[siteunseen]

Here's something to read about tuning your SUs. It helped me enough to get by until I get the DVD from ztherapy.

http://www.classiczcars.com/forums/su-carb-technical-articles/41940-quick-dirty-su-tuning.html

And here's a post on understanding the timing,

http://www.classiczcars.com/forums/engine-drivetrain-s30/51042-reading-distributor-specs-expected-real-world-performance.html

Edited June 24, 2014 by siteunseen

[FastWoman]

I don't know much about carbs, except that I hate them, and they hate me back. However, I'll just mention that the Z distributors are not terribly robust devices. Pull off your distributor cap, and give the breaker plate a twist. It should move smoothly, with no binding. This is a common problem area.

[Thenervemann]

Another question, the valve adjustment.

When I did the adjustment I measured out the distance between the bottom of the lobes on the camshaft to the top center of the rocker arm not the distance between where the rocker arm presses down on the valve and the top of the valve itself. Is this correct? I could not get a feeler gauge between the rocker arm and the top of the valve.

[Thenervemann]

...or was I suspposed to do it like this:

"Valves 3, 7, 11 need to be adjusted when valve 1′s lobe is pointing up. So these four valves can be checked at the same engine rotation.

Valves 5, 10, 12 get checked when number 4′s lobe is pointing up. These four can be adjusted.

Valve 6 gets adjusted with 2′s lobe pointing up. These two..

Valve 9 gets adjusted with 8 pointing up. These two."

Where I THINK Valve 1's lobe is the closest to the front of the car. (correct me if I am wrong.)