My bike's got the shivers

[fazersharp]

Gonna post my issue on here for the wider audience to see if anyone can pinpoint or recognise my bikes problem.


Last couple of weeks my 600 has been suffering from a very mild "shivering" effect at lower revs, and i'm not entirely sure what to do about it or what's causing it?
It's nothing major, yet, but it is there, which means it's bugging the hell out of me.
And it's not a stutter, or a hiccup like you would get with an air leak, but similar to the noise a person would make when they are very cold and shivering, but as stated it's only a mild effect.


Otherwise the bike is mechanically sound and looked after.
Tickover is rock solid, needle doesn't move from 1200rpm, no hunting or anything.
Approaching 49,000 miles, mainly used for commuting.
Recent brand new TPS, in correct position at 5000rpm.
New battery a few months ago, and bike starts first time on the button, no choke needed at all.
K&N air filter cleaned and re-oiled a few weeks ago.
Oil changed within last couple of months, and cooling system is all fine and air tight.
NGK spark plug caps.
Carbs balanced by me 3 days ago, all totally level, which helped a lot but not got totally rid of it.
Quill aftermarket end can, been on there for years though, so totally ruled out.
Mainly happens under 3000rpm, if i pull the throttle back it runs perfectly, no coughing spluttering or anything, absolutely fine with smooth and efficient delivery of power.
Not changed plugs for a while, but i don't do high mileage at all, so although i don't actually think they need replacing i never jotted down when i last changed them, so i've ordered some new NGK Iridium plugs anyway to rule them out just in case.


So, anyone got any ideas at all, 'cos i'm a little bit stumped to be honest?

It must be you then - put your vest on.