Might be the camchain. Not something you want tight enough to lock the engine, even a little.
It could also be the starting mixture pushing back on the piston. There is no info about your engine/ignition so start another thread.
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I can kick my XS just fine, now. I can just see the day where I might have problems. It may be close. I have a friend my age who has a right knee replaced.
I'd like to find a bolt on longer kickstarter. I haven't been successful so I thought I'd ask the hive mind, fishing.
Two stock kickers could be cut and welded but that might not be as reliable as I want. I know how to engineer the part but the welding will need to be perfect and a tension plate welded over to make it as strong as a stock arm.
Tom