Going to ask you alot of questions to try to get more information.the more you can provide the better we can narrow down your problem.Why did you feel you had to pull start it after a new topend? Also why was a new topend installed.did it have the same symptoms you are. Experiencing now? If cdi is bad it won't start . is it getting spark? Somtimes pull starting can shear flywheel key. To check that you need a flywheel puller.Fresh fuel? Carburetor squeaky clean. All jets and holes clean and blown thru. A pluged pilot jet will make it hard to start..new plug. Reeds in good shape and sealing tight.