We have resolved this idle issue on the units that were being affected by adjusting the idle mixture at the regulator. This can be accomplished by knocking out the cap that covers the idle mixture screw on the top of the regulator and turning the idle screw until the unit stops surging. The idle speed may have to be adjusted once the fuel mixture is adjusted. No parts required. This issue may be attributed to the units being set at near sea level and then being put into service at a higher elevation.