Stalls When Braking

[Mulletwagon]

The old four banger starts and idles fine, pulls through the gears like it should and does not miss at all. When braking in neutral, especially aggressively, the engine shudders, loses rpm, and usually stalls but sometimes recovers back to normal idle rpm. Mixture set to a quarter turn and timing about 25 btdc. Thinking a carb problem, maybe float level, but don't know. Looking for a plan forward.