I have been told that these motors do not like 91 as they were designed for higher octane leaded fuel. Try some higher octane fuel or octane booster- this may help with the sputtering under acceleration.*I drained the gas tank last Fall. She sat a lot this winter but I put fresh 91 octane in her over the past few months during my time tinkering. I put a new Toyota fuel filter in recently as well. Does the Weber carb have a fuel filter that may cause an issue?