Acceleration performance bad after timing belt change

I own a Honda Accord 96 LX 2.2 non Vtec, I recently had the timing belt changed. The original belt was still installed and I had a mechanic friend replace it. The car is now performing poorly (mileage 131,100) specifically the acceleration, every time I take the highway pressing the gas revs the engine around 4 to 5 RPMs and the car is slow to accelerate. This was never a problem till after the timing belt was changed. There is no check engine light on and if the gas pedal is pressed fairly quickly the car back fires. If someone can help clarify this problem so I can repair it would be great.

Thank you