i would suggest strip and clean the carbs as a starting point. if the bike previously run fine dont adjust anything. youll just end up not knowing where you are and have a hell of a job sorting any problems.
i have noticed that the american contributors to these carb related questions seem to go straight for the adjust this, change that, fit bigger this ect. rarely is the problem that complicated.
if it was running and then stopped it isnt going to be the size of the main jet or any other jet size issue. it soundls like the carb is running a bit lean due to a blockage of some sorts. my dr regually needs a carb cleaning as i use it a lot in mud, every time i strip it there a lot of dirt in there despite inline filter and filter on the taps.
the knock sounds like preignition caused by a lean mix.
clean the air filter whilst your at it and make sure all breather pipes ect are clear. i would put money on a bit of sludge in the pilot jet circuit, remember to count the turns on the pilot screw and replace exactly the same when rebuilding.
after this you could check the valve clearances and the decompressor cable adjustment. fit a new sparkplug as well whilst your there.
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