Quits how? Burp rich or does it die lean?
Uniflow tanks are notorious for quitting if they develop the tiniest leak in the wrong spot. If you have a leak along the top, back edge, turning a hard inside corner will drop the fuel below the leak and suddenly the mixture changes radically and the motor quits. Just depends on where the leak is. After all, the uniflow vent is just a controlled leak down in the wedge near the pickup.