hmmm I wonder if you have a crank seal gone or your statore could be going as this would cause a weak spark under load , my plug is 7 and il look at it tomorrow to see what its burning like .are you shaking the fuel properly to mix the oil up , how are you mixing the oil and fuel. and are you turning the choke off as soon as it starts and not ridding with it on , sorry for all the questions just trying to cover the basics