My l24 with SU carbs is up and running but I’m having trouble with the air fuel adjustment. I adjusted timing to 5 BDTC and balanced the carbs using a synchrometer. Idle is around 750 rpm. When I use the piston lifter on the front carb rpms increase and then come back down but the engine will then die if I don’t let the piston drop. When I use the piston lifter on the rear carb rpms increase, stay increased (around 1300rpm) and the car backfires. When using the piston lifters ideally rpms will increase and then drop back down without the car dying correct? It seems like the front carb is a bit lean and the rear carb is rich but they are supposed to be adjusted together correct?

The nozzles are normally set 2 1/2 turns down from the top. Have you checked to see what yours are set at? They may not be the same.

I just rebuilt the carbs and started with them both 2 full turns down, but after the above difficulties moved them both to 1.5 turns based on the service manual.

The RPMs should decease when lifting that piston, almost dying out. Lifting the piston disables that carb then you are running on the 3 cylinders the other carb feeds. That's what mine does anyhow. Try reaching in and lift the piston itself instead of pushing those pins down.

Your needle height may be off from the rebuild with the needle height set screw?

Remember raising and lowering is viewed from the bottom of the car. Turn the nuts towards the fender to lower the needles.

Read the section on SETTING MIXTURE.