got a dc2r. a few months ago, there was some heavy build up of black dirt from the exhaust on my rear bar, but it hasn't happen lately. tho, i can hear the car, back fire? its not loud, its like a soft burping noise at low RPMs. anyway i think its doing damage to my spoon streets muffler as i can hear something rattling inside when i start the car

im also getting pretty shit mileage, usually ill get about 380kms out of a tank, this fill up is going to be around 320.

so what are the initial steps to do?

where can i get a tune to fix it running rich, for a cheap price