It sounds like you need to adjust the tracking of the blade.
Unplug the saw and make the adjustments while turning the upper wheel by hand.
On the back of the upper cover there are three knobs: 1) Blade Guard Adjustment Knob to allow you to move the upper blade guide assembly up and down; 2) Blade Tension Knob to apply proper tension to the blade; 3) Tracking Knob to adjust the position of the blade.
1) Set the blade guard to place the upper blade guide assembly just above the work piece. (Pic. 1) Release the thumb screw and move the thrust bearing back away from the blade. (Pic. 2)
2) Adjust the tension as indicated on the scale below the knob. (Pic 3)
3) Adjust the tracking of the blade by loosening the wing nut, (Pic 4) then change the blade position on the upper wheel by turning the tracking knob. Slightly tightening the tracking knob will cause the blade to track more toward the back of the machine. While turning the upper wheel by hand, set the tracking knob so the blade will be running in the middle of the upper wheel. (Pic 5)
Re-adjust the thrust bearing to be just off the back of the blade (1/64 inch). (Pic 2)
Suggestion: When you have the blade off, balance the upper and lower wheels with tire weights (Pic 6). This will greatly smooth the running of the blade.