I just changed out drop bars to bullhorns (Origin-8) on a road bike. I'm experiencing a bit of slip when I pull up on the bars hard while sprinting or climbing.
It's a Nitto quill stem circa 1989 (bike catalog specs list it as a "Young" model). Both stem and bars are 26.0. The handlebar pinch bolt has 6mm hex on top and a nut underneath (clamp is not tapped). There is still a gap on the stem clamp.
I don't have a torque wrench, but I have the handlebar pinch bolt wrist-tight using the Park 3-way hex tool (link).
Can I go tighter? Is there anything I can do to the bars or stem to minimize slippage?