Hi, I assume it has a manual starter. it sounds like the starter clutch has gone. Which is screwed onto the crankshaft on top of the flywheel, under the starter cover. If this is the case the clutch will feel sluggish to spin around by hand. Inside the clutch there is ball bearings which engage the mechanism to start the motor but under speed the bearings flick out due to centrifugal force so the starter then becomes disengaged. what happens is the internal pivot of the clutch as it spins on the crankcase needs to be light lube up with engine oil. over time it may dry out and bind up. The fix is remove the top cover of the clutch, bearings and top pivot. The crankshaft will prob be black, use around 1000 wet and dry sand paper and clean it so its very smooth and silver Wash out the inside of the pivot and clean as best possible. There is a felt pad inside the pivot remove, clean and light oil with engine oil. Make sure the bearings are clean and not oily. Re assemble. If the crankshaft is really scored, you will need to remove all the scratch's, and replace the clutch.
Hope that helps.
Last edited by timtoolman; 23/08/14 07:55 AM.