Bike won't run over 20 mph, sputtering idle

[Shipman515]

Hey ya'll.

My gz250 recently stopped running normally. The bike now sputters when in idle and will not accelerate above 20 mph. It sounds like it is not getting fuel properly (I've tried seafoam and another cleaner, but to no avail). Just curious where y'all would recommend starting to remedy this problem.

Edit: It's an 01 with approximately 8000 miles if that helps.