More like a pre-ignition fire. IN high gear, at about 5000 RPM, when I need to power up , like a hill or strong head wind. I hit the throttle and total power loss for a second, 2 or 3 times till I drop back on the gas, and it makes a strong ping noise at the head. 98 KLX 250. I ws hoping it was something simple like old fuel, but I tried new , highe octane, and the problem is the same

 

sounds like a carb tune up to meet your timing and atmospheric conditions at that moment or where you live.

 

I'd use a strobe to check the ignition timing.

If you don't sort it quickly you're risking a holed piston.

Rob

 

By strobe, do you mean a timing light? I dont think the timing can be adjusted, it comes form a magnito

 

Even with a fixed magneto timing can move because of wear. If the bike uses a CDI it'll have an ignition curve map.

The other likely possibility is a weak mixture. This will also hole pistons.

Rob