Acceleration is weak and fuel consumption is high.

According to your description, it may be:

1, the throttle should be cleaned.

2. Check the cylinder pipeline for leakage or poor contact. If the car is used for a long time, do you need to check the ignition coil?

This may also be the reason why the spark plug turns black:

1. The high-voltage spark is too small, generally because the spark plug gap is too large and there is too much carbon deposit.

2. Too much oil spray or oil dripping from the nozzle, if it is too thick, will cause the mixture to turn black.

3. The ignition time is too late and the combustion is insufficient. This is usually accompanied by sudden phenomenon or unstable idle speed and can't afford to refuel.

Because you can't see the real car, you can't accurately judge the fault. I suggest you contact your local 4S shop or repair shop for testing and maintenance.