HIF6 needle setting puzzle

[gbvona]

The pistons in my HIF6 carbs (AUD623) have a rectangular slot milled in the bottom of the piston, about 2 mm deep, 4 mm wide and parallel to the airflow. It goes all the way across the piston. However, there is a steel insert in the middle of the piston (into which the needle bush is fit) the bottom of which is flush with the bottom of the piston, interrupting said slot in its middle.

The WS manual says to insert the needle guide (bushing) into the piston until its bottom face is flush with the bottom of the slot in the piston. This would set it into the steel insert about 2 mm. I also have an SU leaflet on the HIF6 that says to insert the needle so as to have the end of the straight shank on the needle flush with the bottom of the piston. Since the straight shank of the needle sticks out of the needle guide about 2 mm, this spec would be more or less consistent with what is in the WS manual. Just checking to make sure that interpretation is correct.

And that being said, what is the slot for, since the steel insert blocks it halfway across the piston??

gbvona

PS Was privileged to hit the Goodwood Revival Friday and Saturday. Y'all sure know how to throw a party.

 

[roverp480]

Burlen SU pages , suggest the bushing is inserted flush with the recess.
Reassembly - SU Carburetters

 

[unstable load]

(g) Ensure that the needle guide fitted gives the needle bias in the required sense (either toward throttle disc or toward air cleaner). Before tightening the retaining screw, check that the needle guide is in its correct position relative to the piston face, either flush with the bottom of the piston on standard pistons or flush with the recess on recessed pistons.

From here...
Reassembly - SU Carburetters

 

[cobraboy]

I tried setting the needle guide flush with the bottom of the piston on pistons with a slotted bottom and the car would not run, it has to be set flush with the slot - ie so the slot is not impeded by the guide. This should leave the shoulder on the needle about flush with the very bottom of the piston.
The Revival was great wasn't it ! Last year's got nicknamed the Goodwood Survival, boy it was wet.