Bucking Justy

My manual 1990 Subaru Justy (3cyl) has only 80K, but suddenly started bucking, jerking, and hesitating. As if it's engine is really cold. Even when it's warmed up. As a driver, it feels like trying to get water out of a kinked hose. I need to tease the accelerator to get power. Fuel efficency down about 10%, too. Thanks!

Thanks for responses. We've had it 3 mos. Put on only 2K. It had recently been tuned up according to the seller. We swapped fuel filter from our other Justy, but there's no guarantee that was good. The plugs & their connectors appear clean, but I don't know how good eyeballing is. What kind of carbon removal? There is no ECM (I think), this is an older, carbuerated car.

Engine light does not come on. Air filter looks clean enough to eat off of.