Hi-
Have an all-stock 1999 Scrambler 400 - I live in Tucson but often take it up to the mountains to ride at about 8000 feet. Manual says smallest jet to use is 160 - I keep going lower and lower - gonna try a 135 this weekend, used a 145 a few weeks ago and it still was bogging down at low rpms. Shy of new clutch kit, any other simple mods to make to get more air in at low RPM'S? I know K&N helps at high RPM's, but will it make a difference when I'm bogging down?
Dave

 

you can set the needle jet 1 clip down if you having low rpm bog,meanwhile beware of lean conditions,make a spark plug test at 1/4 throttle setting,check the plug color for proper running.
what do you mean 160 main?? with the stock carb (mikuni 34mm) you need to run at least 230-240 main with stock pipe...later...