Small Engines (Lawn Mowers, etc.): 6.5 ohv tecumseh, no screws, tight spots

Question
This engine runs great at anything above idle but it will not idle, and it has no screws to adjust other than idle screw

Answer
Did the engine idle before?  Does it sound like the engine is running way too fast?  Did you recently mow near, around or under any tight spots that my have bent any parts on the engine?  Did the problem happen suddenly when using the mower or has the unit sat for a while?
Let me know.
Eric