knocking under acceleration
 

my 2005 gz250 sounds like it is knocking under heavy accel i cant pinpoint the sound since i have to be riding it. its kind of a hard high pitched thud and sounds like pre detonation. i dont know how or if you can adjust the timing so i cant check if it is infact pre det. there is also a loss of power at about 1.500 rpm if anybody knows what thats about
the bike only has 4k miles on it

I believe there is a thread on here on how to check and set the timing. Use the search feature.

You may need a valve adjustment if that isn't the problem. There is also a how to here for that. They recommend that you check/adjust the valves every 3k miles, but I have only done it twice and have 24K on my 09 GZ.