[tridentperu]

I had a similar issue with my M600 - very poor running at small throttle openings, running rich, sooting plugs, jerky running, only happy on big throttle openings, exactly what you describe.

I got very very good at taking the carbs off/ and back on again. I cleaned everything (several times), set everything according to the book, fitted new float kits, diaphragms were good - did it improve? No.

I won't bore you with the whole saga but in the end I bought a used set of carbs to try them, but they weren't in any fit state to use, so I kept them for spares.

What was immediately apparent when comparing parts from both were the needles - the needles from the spare carbs were much thicker (visibly) than the ones from my carbs, totally different in fact. I did a load of research and it turned out the the numpty who owned it before me (I bought it cheap it as a non runner) had fitted dynojet needles but left the original Mikuni needle jets in....Doh. Fuel was pouring through it as soon as you touched the throttle!

I fitted the std needles from the spare carbs and, hey presto, smooth running was achieved. That was a couple of years ago now and the bike has run great since, all I have done recently is weaken the mixture a bit on the pilots as it was running a bit rich on the smallest throttle openings, you could tell by minor fluffing and snatching low down - now, all sorted again.

And yes, the grey boxes are important as they allow the vacuum part of the carb, that control the diaphrams, to draw still air when the bike is going. If the pipes are left open to the elements, the diaphragms can go all over the place and upset it even more!

Iridium plugs have helped prevent plug fouling too.

Hope this helps,

Jim