If your friend is experiencing pinging ... questions to ask.
1. was the bike tuned with a power commander race tuner or by seat of the pants or some other method.
2. was there a cam change or any advance gears added
3. was there any headwork done ....
4. Any idea what the bike's static compression is .... based on cam might tell you something
5. Possibility of quick closing intake with over compression
6. Anyone played with the his timing?
7. Have you tried adding octane booster to 93 octane fuel if so does the problem go away
8. Have you run any injector cleaner in the gas?
9. Is it Carb or is it Injected