WAG (wild assed guess), But,, Some carbs have an insert which lives above the emulsion tube/main jet holder. often referd to as a "needle nozzel" which provides 2 functions, 1st, acts as a "needle guide", & 2ndly as a quasi needle/jet /orifice. look to the bottom of your' carb's intake throat where needle enters lower venturi , if it's brass, I'm totally off-base. luck g