That's a huge problem to have a jet lying in the bowl, that jet is there to meter fuel through a very precisely drilled orifice, if it's not there, you're going to have some very lousy running. I'll bet that your carbs have 5181 needles, those are what mine came with. It's actually really easy to check the needles, far easier than messing with the jets, take the top off, slide the retaining clip off to the side, hold the throttle open with one hand, catch the circlip with either a knife blade, or a pick, or something of that nature, and then let the throttle close, and you'll have the needle by the clip. The size will be punched in somewhere. Yes, a big bore kit, with those carbs, will really wake that engine up, don't think of it as "the carbs running better", instead think of it like the engine running better with those carbs AND a big bore conversion.
