hello, followed suggestions and checked out the hyd pump and pulley, also checked on flex plate and all looks ok. also checked ignition wires and they are ok. will replace aftermarket wires with OEM anyway but for now engine is working well. one thing operator told me was that when it started shaking or vibrating he gave it more gas and the vibration went away. i was not able to duplicate vibration while performing troubleshooting and following suggestions. for now, since the units is running fine i will wait for it to start acting up again unless somebody has another suggestion.