Mikuni carb ID and purpose of a brass tube.

Hi Folks. I'm trying to identify the model number of a Mikuni carburettor on my Briggs and Stratton mower motor (1988). The problem is that there is no identifying number or other marks on the carb to help me. The following is all I have "Made in Japan" stamped to the right of the fuel inlet, MIKUNI CORP stamped on the body just above the float bowl and below the idle adjust screw. On the inlet port (24mm [15/16"] dia) beside the throttle assembly there is a Briggs and Stratton stamp with a 'registered' symbol (R) beneath it. The only other mark I saw was the letter R stamped on the carb body between the bottom of the emulsion tube and the side of the carb body where the float bowl fits. It was fitted to a B&S Vanguard V160 single cylinder motor on a Mountfield Monarch walk behind lawn mower. There's also a brass tube that runs parallel to the emulsion tube and I do not know its purpose. I have had the entire unit disassembled, soaked in carb cleaner and thoroughly cleaned. It was reassembled with all new parts from the carb overhaul kit but the motor only runs for a few seconds and then stalls. If I squirt carb cleaner or WD-40 into the air intake of the carb, with the air cleaner removed, the engine runs happily for as long as I squirt. So, fuel starvation is the issue here but everything is clean except... I don't know what the brass tube does. When I search for part numbers for carbs used on my model of mower, for images to compare, I get the modern equivalent, which is unlike my carb. Other similar carbs don't have the brass tube and for those that do, the brass tube is not identified. The tube is about 2mm across and the inner diameter is about 1.5mm.



I'd be grateful for any guidance regarding this please.



Many thanks,



Keith