Motorcycle Repair: z50 engine problem, honda z50, pocess

Question
I have a 49cc honda z50 (1978). It has a new coil, plug, carb, points and piston. The timing is set right (i think). ("T" on flywheel lines up to mark on case and the cam sprocket has a little circle that lines up to notch at the top of the head.) With the plug out, it cranks over fine (no spark of course). But when I put the plug in and try to kick start it, I get one good kick for a turn over, but the second lick seems to freeze up and the kick start just feels like it is stripping of sliding down (no engine rotation.) When the kick start returns to postition the pocess happens again. I am totally blown away. I thought that maybe I had the piston in up side down, put I peeked in with a flashlight and I can see the little arrow pointing down (meaning the intake side is up - I hope.) I noticed on the old piston that one side of the piston had a larger indentation for the intake? valve and a smaller for the exhaust valve.?..
Any thoughts on what the deal is befor I buy another motor?
Help!
Steve S.  

Answer
Steve, yes the arrow goes down towards the small relief of the exhaust valve, so your piston is not upside down. If it was, putting a plug in or not wouldn't make any difference. If the valves and piston were colliding, they do it mechanically, plug or no plug.

You may be experiencing some issues with the kickstarter pinion gear hanging up on the shaft due to wear or damage.
That's inside the cases, so there isn't much you can do, other than check how it may be engaging the transmission and clutch, by pulling the clutch cover. Make sure that the k/s lever isn't stripping on the k/s shaft spline.

If the kickstart shaft stop in the cases is damaged, the shaft will over rotate and jam the pinion gear inside. Perhaps, that is what you are experiencing. Any repairs require a complete motor teardown, unfortunately.

Bill Silver