My car won't run on low test gas it takes fits and sometimes won't hardly pull itself feels like its runing out of gas. Seems to be at a low rpm. Does not smoke and I have heard it backfire through the exhaust sometimes other times it runs fine. On low test gas it will run ok but when it takes a fit trying to get it to start away at a greenlight is a real challenge. It shifts up and down a lot it seems to work better on a higher rpm can you help me.