Small Engine Troubleshooting Problems? Ask a Mechanic Now.
Hi and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, bear with us; re-confirm and post back with the complete model number of the "...Yamaha 8 HP four stroke manual start motors..."
Or if outboard motors, then would have to be re-categorized to the Boat section.
Still, for the description of "... no spark of ignition...", proposed preliminary tries (if have not been done):