Small Engine Troubleshooting Problems? Ask a Mechanic Now.
Make and model? Engine ?
Have you ran a cylinder balance test? Loosen the spark plug wires, and with the engine idling, remove one wire at a time. Engine should continue to run. If engine dies when either wire is removed, the opposite cylinder is not firing. If both cylinders are firing, and only problem is the surging at idle, try taking the slack out of the springs on the throttle linkage at the carburetor. Do not add tension, but take out the slack. But I really think you will find engine is firing only on one cylinder!
OK, I just know how well these engine run on one cylinder, and when they do , they surge at idle. To clean the idle circuit, the carburetor will need to be removed and completely disassembled to clean effectively.
So I assume the cylinders were both firing, and engine did not die. Try a fuel test line , direct from the fuel pump inlet, into a separate fuel container and see if surge goes away.