indicates a problem in the fuel lines to the carby
could be a hole in the primer bulb, split hose
hoses on the carby incorrectly
diaphragm problem in the carby ( real possibility if using e-mix fuel)
probably not as the movement is probably the cause of it not turning
you should be able to turn the attachment by hand before fitting
if the attachment is not the same manufacturer as the power head then there is a possibility that the drive ends are not compatible
There are at least 3 different designs in the end drive