2005 kx125 help

Hey guys went for a ride yesterday on my kx125 and towards the end the bike wound to go into full powerband and almost sounded like it was detonating when I’d try go into full powerband, it went into mid powerband fine and lower rpm but not full power, I’ve recently rebuilt the bike has about 4 hours on it and a bunch of parts lectron exhaust ect, the bike is mint and I looked over all the power valves, cylinder is mint piston is new, had a new coil and Ignition. Before hand the bike was running great although it did sometimes sound like it was detonating a bit when I was in full powerband, bike still has great compression and starts and runs perfectly just doesn’t go into full powerband, I’m thinking something in The power valves is loose or broken as I’ve had the power valve screw come loose before and was a similar situation just didn’t go into powerband at all which is why I’m thinking it could post robot be something else this time as it still goes into mid powerband. I’ve yet to start looking into it but will be today or tomorrow, And tips ? Thanks