If the model you have is the one with internal & external gas tanks, check outter tank internal filter, and both gas filters, one at the bottom of the interior tank key (has a screen), the other seems is a check filter at the cowling entrance, where exterior tank connects, probably obstructed, check blowing both ways.
Your symptoms are typical of varnished-up or restricted idle/slow speed carb passages. What is happening is that with the idle almost inoperative, you are dialing-in the idle at a throttle plate position that is actually sucking fuel through the main circuit. But at slow speeds, it is delivering only enough for a fast idle. Once vacuum gets just right, the carb starts delivering a little more fuel. Since you are not under load, the motor could easily go up over 2,000 RPM. It probably will eventually drop back down again to near where the idle was before.
Get the carb apart, properly soaked and cleaned, and you will be well on your way to a better idle.
If the model you have is the one with internal & external gas tanks, check outter tank internal filter, and both gas filters, one at the bottom of the interior tank key (has a screen), the other seems is a check filter at the cowling entrance, where exterior tank connects, probably obstructed, check blowing both ways.
I think the fuel is flowing freely, there is no hesitation or sluggish behavior even at higher RPMs. (But I will check/change the filter when I take the carb off).
You will know more once it is apart. No special tools needed. Usually no parts needed. You may or may not want a carb kit, as you may or may not have a worn needle/seat, etc.
