Ted, by over richening the jetting to help with the detonation you are in fact de-tuning the engine. Thats not the reason you bought the pipe to begin with right?
I know it must be frustrating, but you bought the wrong pipe. SST's are top end pipes. The factory fatty, regular fatty or the gnarly are good choices. The gnarly is best for the woods.
Let me clairfy some more on the SST's. They are basicly regular fattys with a restricted stinger section. This increases back-pressue in the system that in turn raises the pipe and engine temps. It also provides a stronger than normal return signal(wave) to the exhaust port. This increases the cylinder charge pressure, much like an out of control turbo in reverse.
The problem here is unlike a turbo, theres no way to control this over boost condition and detonation occurs. SST's make great flash numbers on the dyno, big top end gains. But along with this additional HP, excessive combustion chamber heating/detonation occurs that everyone complains about.
The 05 KX 250 comes from the factory with fairly high compression and and what seems to be an agressive ignition advance that pings on pump fuel. This is the wrong type of engine to run an SST on.