I am going to agree with everyone who says the frame might have issues. I had a big red that hit a a culvert while riding in a ditch. The tree was broken at he bottom because the tire was pushed into the frame. The down tube on the frame was broke and the spine on the frame (right where it separated into 2 tubes from 1) was broke. Who ever had welded it back together had it slightly off, the rear tires were exactly the same size, replaced the triple tree and forks. I could wheelie for ever in a dead straight line, but as soon as the front tire was on the ground it pulled hard left. Upon measuring the frame, it was ever slightly longer on one side over the other it was only a couple millimeters off, but it made a huge difference in the handling. I know that a 350x frame is not the strongest and are prone to twisting if crashed hard. Also check your front wheel bearings, i know that can make you pull one way.
Currently : trx400fw, ct70, 250es,200x, xl80s, 350x, 350x, 225DX, trx300