Originally Posted by tedsander

Right away I recognized it as an old OS carb. The upper adjuster with the slotted head is the low speed needle. The forked arm surrounding it is essentially an adjustment limiter - the head of the needle is offset, and as you turn it, it moves the fork one way or another. That fork has limits, supposedly preventing one from adjusting the needle too much in either direction. It was a pretty poor carb, and was ripe for replacing with a Perry or SuperTigre. The engine itself was great, once the carb was replaced. Ran mine for many years.