I am having issues with my DT40. It idles sometimes and other times it won't start. The motor runs great some days but others it bogs down as soon as I advance the throttle. I have rebuilt the carb already and it has not changed. My plugs look great, the fuel filter is new, and the oil is fresh. Any other ideas? I was thinking about replacing the fuel pump but I wanted to get more input before I spent the money on it.