I have an Echo SRM-260 that has a problem that I can't figure out. Cold or hot the motor will bog down when I squeeze the throttle to get the string spinning. I've cleaned the plug, exhaust. gas and air filters. It's hard to start but if I move the choke around after it starts I can get it up to speed BUT IT WON'T STAY AT MAX SPEED UNLESS I TURN THE UNIT UPSIDE DOWN. I'm not kidding. If I rotate the unit upside down it will go to max throttle and stay there for less than a minute - then bog down again and shut off. HELP!