You do not need two vacuum advance lines.
Unisync gauges measure air volume. With two oversized carburetors, the volume each has moving through it will be so low, the unisync tool won't be able to pick it up. It will almost be shut completely just to raise the ball a little bit. When its shut that much, you are now changing the mixture by choking the air flow. I ran twin Monojets on a 250 for a couple weeks. One was more then enough to power the engine, two worked really well at full throttle only. With low air volumes, the mixture was extremely rich, thus draining the fuel tank way faster then I liked. It was using so much fuel I could see the fuel gauge moving! No amount of leaning out or tuning will fix that situation.
I now run dual Carter W-1's off 216 ci engines on a 250. They are just right and work really well for how I have them set up. I still can't use the unisync, my engine idles at 650 rpm and doesn't move enough air to make the tool work as it should. If both carbs are identical, set the throttle blades to 100% closed. Back the idle screw way off so you know for fact the throttles are closed, then bring each stop back in till it just touches the throttle lever. When you have both just touching, turn each screw one turn to open the throttles. You will have to start the engine at this point to set idle rpm. When you adjust one, adjust the other the same amount, it takes time and patience to get it right.
Last edited by Joe H; 03/22/2021 1:18 PM.
