Hi:

I'm reading the carb tuning how-to's on this site and I realize I may be turning the wrong screws and going around in circles. My setup does not have any emissions from (#1 to #6 and #13) in the diagram, so I have four screws I may adjust #8, two #10's and #14 (excluding the mixture nuts but I understand how they work).

Adjust idle fuel and balance: I don't know what the screw at #8 is called but I'm supposed to disconnect the ball and socket there or back off the screw? Then I use the individual screws at #10 to balance air flow and by disabling front/rear. Should #14 be backed off the tab?

Off-Idle Fuel and Balance: Turn the fast idle screw to 3,000 rpm. Is this the screw at #14? When at 3,000 rpm do I use the #10 screws to balance and by disabling front/rear?

Any help is appreciated. Thank you.

Howard

1974 260z

Edited December 4, 20177 yr by 882993md

#8 is the fast idle screw used to recheck the mix at 3000 rpm. It can stick and over-rev so be careful with it.  If you don't already have the FSM download it and print the fuel chapter. It explains the tune up procedure much better than I can.

Edited December 4, 20177 yr by Stanley

You need to disconnect the gas pedal linkage from the carbs linkage that way they are individual instead of working  together as one.  It's the bent one in your photos, from the top linkage to the bottom linkage. Yes you turn #10s to get the air flow equal.  Do you have a way of measuring air flow?  An Empi from amazon.com was a big help for me.

here's something else that helped me a lot

 

Edited December 4, 20177 yr by siteunseen

Synchrometer shown above is better than the other type IMO since it has numbers you can remember or write down.

I think you can effectively disconnect the carbs by loosening the balance screw and fast idle screw. See the FSM:

EF Engine Fuel System.pdf  

 

Edited December 4, 20177 yr by Stanley

993MD

I had to simplyfy and understand this same issue. (1) Each indiviual carb has the exact same adjustments. MIXTURE ADJUST.....25 cents size adjustment that points at the ground. When adusting you must flip in your mind (RIGHTY TIGHTY, LEFTY LOOSEY). My carbs have a small high spot that allows you to better see one rotation as I'm sure all the early SU's do. Some came with an 8 sided adjustment screw which allowed you to see how many FLATS you may have turned it. When making this adjustment make sure the filter is removed so you can actually see what is being adjusted. It sets the intial distance between the needle and the jet orifice. When you pull the choke cable for cold start this opening gets larger thus allowing PERIODIC ENRICHMENT. This is the first setting when synchronizing, as you may have read. If this adjustment is not the same you may never get a perfect balance. (2) 10 & 10 work in unison, enough said. (13 & 14) work together and 13 should set the final balance after you get the carbs snychronized. NOTE TO 993MD...Then bent shaft connecting arm with the plastic socket is incorrect.  This arm may have been installed by a PO because some previous owners didn't have the right length arm or didn't know how to abjust the arm properly. That is probably how the ends got damaged. This can also cause an imbalance between the 2 carbs causing the entire movement to be uneven. Get the proper rod. ZTherapy may be able to help. Thats it. 3 simple adjustments and of course the proper tool and you can set them up. I used to be terrified to make any adjustments but after lots of reading and video watching I have become comfortable tuning these little things. I am looking forward to installing my triples and going to work although some DYNO time is always money well spent. Good luck and GET THE RIGHT ROD.

2 hours ago, siteunseen said:

You need to disconnect the gas pedal linkage from the carbs linkage that way they are individual instead of working  together as one.  It's the bent one in your photos, from the top linkage to the bottom linkage. Yes you turn #10s to get the air flow equal.  Do you have a way of measuring air flow?  An Empi from amazon.com was a big help for me.

here's something else that helped me a lot

 

Yes I have the Empi

Howard

17 minutes ago, esmit208 said:

13 & 14) work together and 13 should set the final balance after you get the carbs snychronized. 

Hi,

i don’t have a servo diaphragm so my #13 is not connected to anything. I”ll order the rod. Thank you. 

Howard

Edited December 4, 20177 yr by 882993md

993MD

I had to simplyfy and understand this same issue. (1) Each indiviual carb has the exact same adjustments. MIXTURE ADJUST.....25 cents size adjustment that points at the ground. When adusting you must flip in your mind (RIGHTY TIGHTY, LEFTY LOOSEY). My carbs have a small high spot that allows you to better see one rotation as I'm sure all the early SU's do. Some came with an 8 sided adjustment screw which allowed you to see how many FLATS you may have turned it. When making this adjustment make sure the filter is removed so you can actually see what is being adjusted. It sets the intial distance between the needle and the jet orifice. When you pull the choke cable for cold start this opening gets larger thus allowing PERIODIC ENRICHMENT. This is the first setting when synchronizing, as you may have read. If this adjustment is not the same you may never get a perfect balance. (2) 10 & 10 work in unison, enough said. (13 & 14) work together and 13 should set the final balance after you get the carbs snychronized. NOTE TO 993MD...Then bent shaft connecting arm with the plastic socket is incorrect.  This arm may have been installed by a PO because some previous owners didn't have the right length arm or didn't know how to abjust the arm properly. That is probably how the ends got damaged. This can also cause an imbalance between the 2 carbs causing the entire movement to be uneven. Get the proper rod. ZTherapy may be able to help. Thats it. 3 simple adjustments and of course the proper tool and you can set them up. I used to be terrified to make any adjustments but after lots of reading and video watching I have become comfortable tuning these little things. I am looking forward to installing my triples and going to work although some DYNO time is always money well spent. Good luck and GET THE RIGHT ROD. I use this type of sync tool. Old but effective. https://mossmotors.com/carburetor-synchronizer-tool?utm_source=google_shopping&gclid=Cj0KCQiAgZTRBRDmARIsAJvVWAsCw0KS1lsfwWsnJwij7wq3qw2Bzh0r_z-Yiwoj376M1dnFQMjuYWQaAkyBEALw_wcB

Edited December 4, 20177 yr by esmit208
Incorrect link

Correct, with the pollution controls removed, screw #13 is no longer part of the equation and can be ignored...that part of the linkage is just flopping around with nothing to do.  It's simple:

0.  Check float bowl fuel level and make adjustments as necessary.

1.  Back off screw #8 fully

2.  Balance carbs with screw #10 to the correct idle speed.  (adjust mixture at this stage)

3.  Increase engine speed with screw #8.

4.  Balance carb linkage with screw #14.

5.  Back off screw #8 fully.

6.  Done.

Edited December 4, 20177 yr by David F

If you use the "Snail"   flow tool, it is designed for single cylinders (Weber DCOE typically) so the flow from the 3 combined cylinders drawing from each SU carb on a 240z makes it "pin" easily at >2000 rpms.

 

Some of these snails have a hole in the side that can be exposed to reduce the air through the meter at high rpms.  (see the hole in the side below).  You may have to punch a hole in the inner rubber to make it work.  Just rotate the inner rubber to close any hole you make.

 

6 minutes ago, 240260280 said:

If you use the "Snail"   flow tool, it is designed for single cylinders (Weber DCOE typically) so the flow from the 3 combined cylinders drawing from each SU carb on a 240z makes it "pin" easily at >2000 rpms.

 

Some of these snails have a hole in the side that can be exposed to reduce the air through the meter at high rpms.  (see the hole in the side below).  You may have to punch a hole in the inner rubber to make it work.  Just rotate the inner rubber to close any hole you make.

 

That's a darn good idea.  My Empi snail maxes out when I do the high speed balance.  A hole will be drilled. 

Yep, a hole in the rubber for me.