Real1shepperd,
You said,
I haven't been able to wreak the full RPM range from my speed changer.
I am curious what speed ranges you are getting.
The Belts should be 4L220 and 4L250. The original sizes were 4L225 and 4L 255 but are hard to find. If you bought them from Skip, they should be correct. Some belts may vary in that 4L width.
Instead of painting the pulley you could use something attached to the Quill's Spindle with more contrast. I have used an Arbor that has the black protective coating for that contrast.
A possible cause is the spacing of the Floating Pulley Assembly. The outside sheaves should have the one belt almost touching the shaft while the other runs close to the outside edge of the pulley. If the one belt is touching the center shaft that could cause slippage. Are the belts sitting close to even with the outside edge of the Headstock and Motor Pulleys? In the picture below the Belt on the Headstock is just shy of even with the outer edge of the pulley. Those are new belts in the picture. Again, belt widths may vary. A narrower or worn belt will sit down further into the pulley.
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Another possible problem could be old, worn or simply bad bearings. That would put extra work on the motor.
As the Speed Changer Chart says
All above speeds are only approximate and may vary according to belt tension, or wear, or current voltage.
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Below is a PDF replica of the Speed Changer Chart.
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Speed Changer Chart.pdf
