the slow jet sits in a recess you must be talking aboiut the main jet just loosen the jet holder and turn the nut down then tighten up the holder and put the new jet in. it should be about 1/8" above the bottom of the bowl where the drain plug is. what is your altitude? anything below 300ft is a 128 main if you are above 300ft 118 and if there are any mods then you need to be larger on the main. a 35 or a 38 isnt going to make a whole lot of difference the slow jet only controls start to just above idle.