gen11

Hey everyone am new and am here for some help concerning a generator am having a problem with. The problem is when the client is on main power all the appliance works ok but when it switch to genset all the cfl and led lights would start flickering. I disconnect all the load and connected just one led and one cfl lamp. Generator was started and both lights was still flickering, stability on avr was adjusted and am having the same result. The voltage and frequency both are stable the only thing is that the engine is two cyclinder. I don't know if that could be the cause. Please help

Thanks