Hey guys im new to the forum. Just bought a 2005 400ex. Its bone stock and not running. The last owner ran it out of oil until the piston and cylinder wall were so damaged it lost compression. Im going to put a 416 piston in i believe and keep the rest of the bike stock for now until i get more cash. So just curious where to start with jetting or is the factory jetting still ok?

 

See how it idles,accelerates with stock jetting plus kill it at high speed,stop as soon as possible. Let it cool down a bit then check the plug color. Should be a light brown to medium brown color. If plug is whitish,main jet would have to be bumped up. See if this chart may help also. Check against your jets as the chart could be off. Plus a good place to get jets if you can't find them locally.https://www.jetsrus.com/a_jet_kit_at..._1999-2008.htm