2002 DWG Running Rough

My son recently had his 2002 DWG in for 10K Service. Bike ran fine prior to having 10K Service performed. Now it is really running rough, backfiring, spitting and sputtering etc. He lives in Hawaii where temperatures stay pretty much the same. The bike is carbuerated. At about the same time Hawaiian Gas Stations all went to a 10 percent ethanol/gas mixture. Would the transition from gas to ethanol/gas mixture cause the problem, and could re-jetting the carbuerator cure the problem? I have had to use ethanol/gas out west in two of my bikes, both EFI and have not had any such problems. Any ideas. John

I have worked on a few ATVs with CV carbs and I know some manufacturers do not recommend ethanol because it will make the rubber and plastic parts in the carb brittle but that usually takes some time. Ethanol is a cleaner my guess is that you had some gas deposits(varnish) in the tank or carb and now the ethanol has cleaned it out or dissolved some of it. Some of the deposits may be resstricting a jet or air passage. You can run it a while and it might come out of it if the varnish isnt to severe otherwise you might have to pull the carb off and clean it.

Thanks for the feedback, sounds like a possible cause to his problem.
John