Gday all,
so I'm at a bit of a head scratcher here. I have a 2008 KX250F which I brought with about 25 hours on rebuild (brought not running which was because had sat with fuel in carby for about 1 year and was sludge). Now at random intervals or just sometimes when I start it on random days it just bogs really hard, like on a flat road with throttle wide open I couldn't get above about 70kph, but when it's running good it bloody flies. Hitting top gear limiter in no time. Now things I have done are as follows:
full professional clean and rebuild of carburetor
fixed small exhaust leaks on header
Fully cleaned fuel tank
And some other small things I've forgotten.

I'm just at a loss at why is happening. When its bogging and I have throttle wide open I can fell start to jerk like the powers there for a second and then sometimes the power comes back and sometimes it stays bogging.

Only thing else I could think that would be worth knowing is a lot of like dirty oily substance is coming from somewhere and I cant seem to track down where it's from.

Also have added inline fuel filter, new air filter. Not thinking spark plug because when the clutch is in or is in neutral it hits limiter with no problems what so ever

Cheers all,