syncing rear carb

[cab]

the video i watched you need to do the 4 center stacks,thats how i do mine
get the 2 on one side to pull the same #'s and then the other side to pull the same #'s could be 5 on one side and 7on the other then i balance the two sides with the center rod and set idle.the other 4 should all be the same.

[zrayr]

Originally Posted by cab

the video i watched you need to do the 4 center stacks,thats how i do mine
get the 2 on one side to pull the same #'s and then the other side to pull the same #'s could be 5 on one side and 7on the other then i balance the two sides with the center rod and set idle.the other 4 should all be the same.

they won't be exactly the same, and since the IDA 48's have no air bleed adjustment to compensate for differences between the two venturies on the same carb (unlike some other Weber models), there isn't much you can do about it w/o some re-engineering. The difference, if any, will be negligible unless there is a mechanical flaw in the engine causing the adjacent cylinders to draw differently.

so for all practical purposes, just measuring the middle four venturies is sufficient. And that's the method prescribed by Jim Inglese as well.


Z.

[dallas_]

Originally Posted by zrayr

The difference, if any, will be negligible unless there is a mechanical flaw in the engine causing the adjacent cylinders to draw differently.

so for all practical purposes, just measuring the middle four venturies is sufficient. And that's the method prescribed by Jim Inglese as well.

Agreed.

You should not have to place the synchrometer on the 2 throats under your cowl.

Take a reading on the carb connected to the main linkage. The second throat on that carb is controlled by the throttle shaft so you don't need to adjust that one.

Adjust the adjacent carb via the attached throttle lever to match. The back throat (the one under the cowl) will follow via the throttle shaft so you should not have to adjust the air flow on it.

Follow the linkage and adjust the 3rd carb, then the one attached to that one via the throttle lever.

You really only need to adjust the air flow on 4 throats as zrayr says.

If the attached throats don't match up you probably have a problem with the throttle shafts binding.

John

[Eljaro]

I have found that sometimes you have a 48 IDA Weber with different synchrometer readings on each of the two throats.
You can get that fixed by slightly twisting the throttle shaft such as to achieve perfect matching vacuum rates.

[Gaz64]

And most of the time, a throttle shaft gets twisted from the throttle lever retaining nuts being tightened without any thought as to where the torque load is going.

I'll reread this thread after I add this.

I'll have a guess and say that the rear barrel flows more than the front (LH bank; and the opposite for the RH bank) and I'd bet in most instances, this is the case when there is different flow within the same carb.