they don't have weight restrictions--it's size restrictions (obviously a 6 foot 5 guy who weighs 275 is going to be *skinnier* than a 5 ft. tall woman that weighs 275...she's going to be much bigger around, ya know. (Speaking from a round woman's stand-point here, tehehe)
Anyway, the size restrictions have to do with will you fit in the ride vehicle, and can the safety restraints/safety bar/safety harness lower or fit properly for safety. So there are a fair number of heavy folks that can still ride, while others have the fluffs in the wrong location.
There are test-seats outside most of the rides at Universal where size will be an issue. So you can try it before you get in line.