I did some research on the buggy you have and apparently the engine in it (.15xcp) only has 1 needle a HSN or main needle to make any mixture adjustments. This high speed needle points straight up from the carb, you cant miss it. That nut you are talking about I think just holds the the throttle linkage onto the slide carb, I tried findin pics of it online but there are not many good ones to look at.