Been working on a 97 GSX. The GSX is in good shape but has been sitting in a barn for 3-4 years. Siphoned gas, and refilled. New Battery. Replaced dry rotted wear ring.

During test ride, lost power after about 10 min of riding. At full throttle, only hitting about 4000 RPM.

Guidance on possible causes?

Also, owner really wants to see the GSX. Anyone interested?