I eventually settled into a higher level of economy with the navigational routine, regaining a bit of composure with each accurate calculation. The plotted-fix spacing was narrowing, though, suggesting either we had slowed or a headwind had picked up. Glancing down at the tachometer I read only 1,950 rpm, and I reminded Mike to keep it at 2,100. After he pointed out he hadn't changed anything, I prompted him to check for carburetor ice. The instant he pulled out the carb heat knob a period of violent coughing and sputtering ensued, which at 200 feet over water provided us both a crippling adrenaline rush.