The bracket is available at J&P Cycles: https://www.jpcycles.com/product/400-0088/todd-s-cycle-choke-relocation-bracket for all Mikuni carbs.
Relocates choke cable and knob out of the way.
For use with stock choke cables and knobs.
Made from stainless steel with a ball-burnished finish.

Below, this bracket has been installed on a HSR-45.

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The coil was relocated to the left side where the choke used to be.
This homemade bracket will help to relocate the choke to the right side between the tank and the top of the carb.

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The bracket was pre-made with a drill-press, band saw, files and belt sander before pics were taken.
It was made from a piece of aluminum (1-1/2“ x 1-1/2” x 1/8“).

Pictured is a top view of a before part, the lid off the Mikuni HSR-42, and the finished part.
3rd pic below is the bracket in place on the lid.
A hole was drilled (1 size under 3/8”) and a band saw was used to make the slot.
The bracket was cut shorter and dressed up.

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This is the top view.
A punch was used to mark the locations of the holes. Note the notch in on the lower right, it's clearance for the accelerator pump adjustment.
Slightly longer button head screws (M4) were used to attach the assembly.
As you can see, the 'ears' were shortened (leaving as much meat as possible).
This also shows that 1“ material would be fine to use.
The small web left at the bottom rests nicely on the lid which helps out.

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Here's a few shots installed with a custom round air cleaner. The choke is on center.

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• HSR Choke Cable Installation Tips