Billerica yamaha Charged for repair that lasted an hour billerica Massachusetts

 I took a kawasaki dirt bike there for repair. I wanted an estimate before they fixed it. 2 days later they call and said it was done. He told me it was dirt in the carburetor, they cleaned it and the air filter and put a new spark plug in,I also had them fix a flat tire. The bill was $274.00. When we picked it up my son test rode it but only had a small residential street to try it on. The bike didnt gave enought time to even get hot but ti seemed fine. A couple days later when it wasnt so cold out my son took it out to ride. He got an hour of use and it started popping again. I called and talked to joe in service,after explaining this situation he said its probably more dirt in the carburetor(why didnt they  check to see where the dirt came from ?) and then went silent . I asked if they could take care of it and he said sure, I then asked if this is going to be more money and he stated of course it would. They didnt fix the problem why should it cost more ? I guess im paying for someone to learn how to repair bikes ? If this report stops one person from wasting money there it will be worth it. I will never step foot in there again and will make sure I let everyone know about this experience. I want to call the owner(met her at the new england boat show in boston last year) but after reading other bad reviews it seems like she doesnt care about the poor quality of service they offer.