i have a small techumsa engine on my go kart and i had just takin it out of storage in my back yard and covered with tarp when i uncovered it and started it up it sounded great then while i was driving it for after about ten minutes i herd a rattling then a huge cloud of gray smoke came out of the enigine then i checked the oil and it was good then i tried to start it but there was no tension when i attempted to pull the starter cord what happened?
make sure the pull start is engaging the motor and then while trying to turn engine look at the shaft and see if its moving where the clutch engages the axle
if not the crank is proably broke ...tear down is the next steo but proably more cost effecent to replace the motor ..might try ebay