Motorcycle Questions? Ask a Mechanic.
Hi and thank you for your question.
My immediate reaction without further investigation would be you have developed an intake leak. The easiest way to find an intake leak is to start the engine and let it idle, even if you have to turn it up a bit above normal, just so it holds a somewhat steady RPM.Spray contact cleaner around both intake manifolds where they contact the head and where the carb is inserted. If the RPM's change with the spray, you have an intake leak. It doesn't matter if the engine revs up or dies, any change indicates it is sucking in the contact cleaner and also sucking air, leaning out the mixture which presents itself as the symptom surging idle.
Let me know how that goes and if you need more help, we can take it from there.