i too have the hk classic straights but i also added a baron's BAK intake so i did what the kit suggested and installed the stage 3 kit (stage 1 if i didn't have an intake) been running it for a week without problems. 4th clip at 2 1/2 turns. funny thing, called 2 dealers and they wouldn't install a jet kit. maybe it must have been a warranty issue with aftermarket parts.
I put on HK 2 1/2" american classic and an air kit from Thunder. We put on the air kit and I had alot of backfire so I called Thunder and they said I needed a stage one kit. Went to the local dealer and they put it in without any hassles. The only problem with the kit was the service guys seemed liked they did not know what they were doing. Took them a week to get it right. Now it runs great.