KX250f Mystery problem

Hi I recently bought a really really clean 2011 kx250f that was completely rebuilt by a mechanic. I took her to the track and it ran absolutely perfect and sounds awesome, but we had the common oil leak problem from the sparkplug weep hole on the right side of the cylinder so we took off the valve cover and put sealant on the top o ring right below the valve cover (the only thing we did) and we think it fixed the oil leak problem without having to take off the cam caps to get to the second o ring, but after reassembling and putting the gas tank back on we started it up and it ran horribly almost sounds like a misfire and is blowing white smoke out the exhaust, which is neither coolant or oil being burned for sure, so it has to be fuel? Also my timing is perfect we never did anything more than taking the valve cover off and now its running so off and wont idle, you have to play with the throttle to keep it running. I'm so stumped any ideas? Fuel injector problem? Spark problem?(I never did end up changing the sparkplug, and oil did leak into the sparkplug chamber cause the leak) Also here is a video of how its running with sound. https://youtu.be/T0vNBR_dXKg




Any help would be greatly appreciated before I take this thing to a shop....

TLDR: Bike ran amazing, Wanted to fix easy oil leak, took off fuel tank completely, took off valve cover and nothing else, added sealant to o ring right below valve cover to prevent oil leak from weep hole, reassembled fully, doesn't run right, misfire? didn't change/mess with anything to cause a problem like this but here we are.