I have been trying for awhile now to eliminate an idling problem. The engine will run fine at idle at one stop sign and idle high at the next stop, or idle fine at many stops and then idle high again. Sometimes there is a slight increase in the rpms when the idle is high at a stop. Recently, I was told that on one of the SUs the solder on the poppet valve has broken away, allowing an unwanted airflow. Until last week, I never heard of a poppet valve! The valve needs to be resoldered. Can this be done by removing the carb, but not taking the carb completely apart? Is it easier or better to install a solid butterfly? Are there other solutions?

Some background:
Complete rebuild of carbs last summer, no idle problem for months afterward.
New PCV and all vacuum hoses replaced, no vacuum leaks detected.
I took apart and cleaned the carbs last week in case there was some dirt in- volved, the engine idled okay for about 1/2 hour.

Thanks