Check the fire of the plugs for a consistent blue spark when they are out of the cylinders.Then i would check the compression on both cylinders with the plugs out and a compression tester installed.Make sure to hold the throttle wide open when testing each cylinder,there should be at least 120 psi in each cylinder to ignite in the cylinder.If not the upper top end of engine is in need of repair.Also check the engine stop switch ,it may just be in the off position or a bad ignition switch.Had that happen on my 77 kawie sst440.Hope this can help you ,good luck.