Engine missfires over 6000 RPM.

[HannesDTX]

Hey guys, so i got my 2006 DT125X about a month ago. It has ran perfectly except a couple of fouled plugs (2-3).
But yesterday it started missfiring around 6000RPM and i cant get over it. The bike starts jerking but it doesnt feel like a carb issue. I thought it was just another fouled plug so i changed that out to a NGK BR9ES. I also cleaned the carb for good measures but no luck. I can also hear the powervalve priming when turning the ignition on.

What could it be?

[Calum]

I mean it could literally be anything.

You shouldn't be fouling plugs, ever...

So something isn't right there

Is it smoking excessively?

Are you losing coolant?

Are you losing gearbox oil?

I've had something similar when I fitted a cheap chinese knock off 'racing' coil, so make sure you have a genuine 3RM coil fitted.

Make sure the exhaust is cleaned through.

Make sure the airbox and inlet tract is cleared through.

Measure the HT lead resistance make sure it's within spec.

[HannesDTX]

@Calum Not leaking any fluids. No more smoke than the regular twostroke. Also a knew airfilter is fitted.

[Calum]

Have you got access to a compression gauge? Can you measure the health of the engine?