Motorcycle Repair: Superglide valve pinging, harley davidson service, twin cam 88

Question
I have a 2001 Superglide with Twin Cam 88.  It's pinging like it needs a valve adjustment, but there's no valve adjustment procedure in my Clymer's.  How do I troubleshoot/fix this problem?

Mileage is 23000, I got it when it had 20000.  

Otherwise runs great, no apparent loss in power, but highway mileage has dropped from 44 to 38 mpg since the pinging started.

Thanks,
Dave

Answer
First off throw your Clymers manual in the garbage. That is where all them clymer manuals should go. Buy a Factory Harley Davidson service manual if you really want to work on your bike correctly. The pinging is from bad fuel or to hot of plugs or retard the timing a couple of degrees, Pinning is not from impropper valve adjustment.  Johnny