I dont think it is linked with the oil.
I see that your new carborator is on the way for installation.
I hope it works out well; if it does not work as desired then;
Write an official complaint to Suzuki for the issue attaching all the evidence and paper work of work done.
get in touch with the customer service to get the issue resolved with the reference to your complaints and workshop visits if not helpful then the best way is to let them know that you are going to the consumer court to pursue this matter. Also state to them in writing with the fact that you are not satisfied and going to the consumer court to further pursue this matter.
File a compliant with the consumer court with all the evidence.