ef3000iSEB: fluctuating engine speed in economy mode w/no load

Greetings.  When in economy mode, w/no load, my ef3000iSEB fluctuates engine rpm.  Revs up, then slows down, revs up, slows down, up, down, up, down.  If I put a load on it, in economy mode, it'll even out..most of the time but will still fall into the surging sometimes with a load.  I've disassembled and cleaned the carb thoroughly; ensuring all jets and passages were clean and clear.  This had no effect.  I'm currently adjusting the valves, which appear to be on the loose side, and have a throttle control motor on order.  When the genset is in normal mode (economy off), it revs up nicely and holds a steady rpm.  If any of you have had this issue and can short cut my troubleshooting, I'd appreciate some guidance.