Could be a vaporizor problem.....could also be a trim valve problem...if i remember right there are two trim valve that have vacuum lines to them they should be located close to the vaporizor....also in the vacuum lines to the trim valves is a Y fitting and a check valve/restrictor valve...these get gummed up and need cleaned from time to time...again if memory serves me right the only thing we used to clean the trim valves and the other parts was diesel fuel...anything else used in the trim valve would guarantee you to replace it..can try cleaning or just replace them from the start of you believe they are the problem...