this is what I use, and everybody else I know. Pelican sells it. Write synchrometer in parts search.
I use two of them. Less aggravation than moving a single one around. They flow equally and easy to test on same air horn.
A good seal to the air horn isn't the easiest to attain and sometime a pia, but it's doable.
a manual throttle is great to have especially when setting up carbs.
