Another method to determine whether the main jet circuit is correct is to pull the pipe off the bike and look down the header tube a few inches. On 2-strokes, a properly jetted engine will leave only a slight amount of ashy deposit in the header section. You want to see very light tan. Black or dark brown = too rich; perfectly clean = too lean (although this is perfect, this leaves no room for error like colder or denser air). Using this method eliminates possibility of the fuel additives giving false plug readings. In short, as long as there is a very light tan ash inside the header, you are close. Another benefit of this method is you don't have to keep installing new plugs to get readings. Even if the jetting has been rich and is leaned out, this section of the pipe will clean up very quickly to give an accurate reading.