Can't sync first carb to others (webers)?

[chaseincats]

Hi guys,

My pal just got brand new triple webers going (74 260z) and we're having a tough time getting the first carb (one closest to the firewall) to sync with the other two.  When we popped the vacuum gauge into the front of each carb, we originally had a reading of "5" for the front two and "7" for the one near the firewall.  After turning the screw up on the other two to "7", the carb near the firewall started reading as "10" even though we didn't make any changes to it.

Any idea what we're doing wrong here?

 

-chase

[240260280]

Balancing air flow and mechanical linkage in triple webers:

The problem is usually the linkage. 

 

Balancing Idle

1.Warm Up and Idle

2. Disconnect the push rod links to each carb

3. Balance the airflow using the idle stop screws

     if one throat in a carb flows more than the other, and the carbs have the air bypass passages (such as DCOE 151 or 150), adjust the lower flowing throat's bypass to match the higher flowing throat.

4. Once all 6 are balanced, give each carb a push on the throttle and see if the flow returns to the same point.  If not then the throttle valve return springs in the carb are most likely weak.

5. Repeat until all are the same.

 

Balancing Off-Idle

1. Set all push rods are the exact same length. One way is to put the 3 rods on two parallel screw drivers, it should be obvious if the rod lengths are different.

2.  Carefully re-install the 3 push rods but do not  disturb the idle air flow.

3.  Push and lock the throttle to 2000 - 3000 rpm then ensure the air flow is the same for all 6 throats. 

     if not then re-adjust (lengthen)  the lower flowing rod and repeat the above steps for Off-Idle

Edited June 7, 2019 by 240260280

[chaseincats]

43 minutes ago, 240260280 said:

The problem is usually the linkage.  Once you get the car warmed up and idling, disconnect the push rod links to each carb and and balance the airflow using the idle stop screws.

 

Once balanced give each carb a push on the throttle and see if they return to the same point.  If not then the springs in the carb are most likely weak.

 

btw if one throat in a carb flows more than the other, and the carbs have the air bypass passages, adjust the lower flowing throat to match the higher flowing throat.

 

Repeat until all are the same.

 

The next step is to make sure all push rods are the exact same distance and reconnect without disturbing the idle air flow.

 

Once this is done, push the throttle to 2000 rpm then ensure the flow is the same for all 6 throats.  If not then re-adjust the lower flowing rod and repeat the above step.

Sounds good, thanks so much.  Will report back.

[hatepotholez]

On 6/6/2019 at 2:33 PM, chaseincats said:

Sounds good, thanks so much.  Will report back.

any updates? Thx!

[chaseincats]

24 minutes ago, hatepotholez said:

any updates? Thx!

Sorry I forgot to finalize this topic.

What it ended up being was a huge vacuum leak in the brake booster which just so happens to plug into the carb that was giving us trouble.  After we replaced the booster, we were good to go.