[drolston]

Take whatever time needed on the bench to get the progressive linkage set up perfectly, so that both end carbs are precisely and fully closed at idle, with the idle adjustment screws backed completely off. Do that with the carb tops off of the carb base so that you can easily see the throttle plates. If the throttle plates are not perfectly centered or stick a little, fix them. Completely close the idle jet adjustments on both end carbs so that idle adjustment is all on the center carb. Don't go cheap on the progressive linkage as the cheap stuff tends to flex and adjustments slip. One of the end carbs pulls or pushes the other end carb; you can take the accelerator pump spring off of (or simply unhook) that carb to lessen the strain on the linkage.

I put 2" risers on my tri-power, which enabled me to invert the progressive linkage. That way I could use banjo fittings for plumbing fuel lines to the carbs, and I could retain the manual throttle control on the center carb. Took just a little grinding on one end riser and the underside of the fuel pump to get clearance for the linkage.