Mate i went through the same ordeal,and yep the battery strength plays a big part for start up on the older motors,i had tryed to start on rather flat battery would turn fly wheel but would not fire,then recharged battery and boom,away she went,i was evn advised dont know how true it is but the volt difference you put out with a semi flat battery can also damage your stator+coils or power pack dont know how true but better safe then sorry,good luck buddy,