Hi.
First, check to make sure that Video Speed sync is enabled under CPU menu.
You can change the timing by setting a different counter factor under Rom Properties. In game, you can also change this by holding down CTRL and choosing 1-8.
As a last resort Under rom properties if you wish, you can manually set the VI limit to 50 under ROM properties.
There are other ways to slow games down by using plugins but what I've listed should do for now. Good luck.