[Paul_E_D]

Get a dremel and slot the screws using a cutting wheel. you'll still need to be careful with the flatblade getting them off, but it will work. You need to take the pilot jets out to clean.

But you need to take the head and cylinder off your bike to find the real problem... It's not gonna be cheap or particularly easy. I think you'll need new rings, and possible a piston and some cylinder repair.