This is weird,the only reason i can think off is that the cdi is retarded and the engine is turning over the right way then firing and spinning back the other way.try this but its a bit tricky.take the magneto off using the correct extractor then take the woodruff key out and move the magneto slightly against the rotation of the engine and do it back up this will determine the problem but its not a permanent fix as the magneto can slip.you could also slot the bolt holes in the stator plate and turn that against the engines rotation this will also advance the timing dont go to mad with it though just a little bit .to do it properly you need a timing light and to make a firing mark on the magneto as i think they only have a tdc mark.i ahve seen this a few times but its not common seen it on a gs 125 and a xj600 pre diversion and an et4.
adam bike doctor
April 2010