Rockwell Wood Lathe

I recently purchased a Rockwell Lathe joinery at a local school. I can not find any model #, but the closest I think it is a model 46-450. This is a variable speed - the button called 340-3200 rpm. It has a 1HP 1725rpm motor, currently wired for 120V (I can rewire to 240 if necessary). My problem is that when running, and I put a tool in Woodstock, I can apply enough pressure to stop the engine (and it does not take much - I trim a little wood off, then wait until the engine before turning back again). Is this an engine problem belt problem, or some other problem, I have not discovered? There is a line that has something to do with the party variable speed in front of the engine, and it is cowardly. I have not been able to shake at any speed. Any suggestions on where to begin to repair the problem?