it is difficult to determine your fault but would check all fuel piping in and around the engine bay and have a look for chaffing/rubbing through,make sure unions are tight,I think some of these had a hand primer also and that is a prime region for drawing air,make sure your filter is clean and all seals round about there are secure. good luck
cdc
February 2013
howtomendit.com for free repair help, information and advice.
