250-500cc Inlet leak symptoms?

Hey guys, have an ongoing issue with my 09 Wr250 that I need to get sorted this week or its going as its driving me mad. Basically, at barely opened throttle (0-5%?) she pops, farts and generally carries on. With supermoto wheels on this makes it downright dangerous, as you cannot corner quickly and roll on smooth.

Other than that I love to bike. I have a chance to pick up a race prepped '12 CRF450 for a steal, and While I've always said I'd never own a Honda, the issue is driving me mad.

I switched to a Lectron, have adjusted both it and the factory carb a million times to no avail.

My last thought is maybe there is an intake leak. I always thought this would affect the whole rev range or at least the top end more, but now maybe this is it. Bike starts first kick every time, runs brilliantly. The plug goes from brown to black depending on the jetting (now perfect brown, love the Lectron) but the plug ALWAYS has a very thin white ring around the outside of the electrode.

I can set the card 1.5 turns rich or lean and it still has the same white ring and symptoms.

Hoping this rings a bell with someone before I crack it and just sell the thing as otherwise it's my perfect bike.

Thanks guys.

check for grounded wires in the harness by the coil.sounds electrical to me.

could be timings retarded a touch, yank the rotor and see if the stator plate has shifted, check the manual for initial set up center punch where the stator is at the moment and then adjust, so you can always go back to base setting.
has it always been like this or is it a recent occurance?
check wires and fuel mix too..

air leaks cause more issues when wet i find, as they suck water in!

Thanks for the advice guys, maybe find a better mechanic to have a look.

I would have to agree with the ignition or timing problems as an air leak will cause a lean condition. Check plug cap and wire for wear and then move onto wiring to the coil and ignition module. The worst case scenario I have seen with similar symptoms was a twisted crankshaft but that was on a 3 cylinder snomobile don't think it'd be an issue for a single.