For your main jets you have to pull the plug on the bottom of the carbs. it is a 11/16 or 17mm. you will have a main jet tool in your tool holder on the sled .shut off your fuel and unscrew the jet, along will come another brass peice.do not let these fall into the belly pan they are brass and not magnetic.when you tighten the correct jet do not overtighten it, they are brass and very soft.For a stock 98 zr500 you can run 340 main jets from -10 to 40 degrees.Also you should check your jet neddle setting on the slide. To do this unscrew the top of the carb. carefully compress the spring toward the cap,and remove the big cable guide, it looks like a big washer.unscrew the phillips head screw,and remove the aluminum peice that the phillips head was holding.you can now get out the jet neddle and see what position the clip is in,for a stock 98 500 it should be in the middle unless it gets warm (above 30 degrees)than you can raise the clip 1 poistion which lowers the neddle,and will lean it out a litttle.I leave mine in this positon unless it gets below 10 degrees,but becarefull,most people just leave this in the middle position all the time.When you put it back together be sure to have the little plastic washers ,one on top ,one below the clip.There is a grove machined into the slide,make sure this is lined up with the little pin in the carb. and it will slide right in.Also remember that the jetting I reccomend is for a stock 98 500 at basically sea level.( wisconsin,michigan ) riding.