engine noise question

[Anonymous]

My 650 KATANA'S engine makes a rattling noise when I'm doing over 75-80kph ,It doesn't do it when it's cold or when it's under load or backing off ,It only does it when I'm cruising at a constant speed ,anyone help ??please.

[Dink]

Is it always at that speed? as in regardless of engine speed of gear?
Dink

[Anonymous]

yes, under 70 it doesn't make a sound.

[Dink]

It may very well be a jetting problem as the speed you mention is on the overlap between idle circuit and mains, provided this only happens in top gear.
Dink

[Dink]

If you can replicate this problem in a different gear but the same engine revs then your carbs need a thorough cleaning , particularly the idle circuit and progression holes, if not you have worn bearings in the motor and this is the "sweet spot" for them to be noticed, in a GS series bike it is most likely the gearbox bearings. these can be changed without a toal engine tear down, you only need to remove the lower case and free the gearbox shafts , swap the bearings and re-assemble.
Dink

[Dink]

Another thought! your Kat 650 is shaft driven. have you checked the shaft for any play or sighs of wear in the bearings?, try draining the oil and changing it to a synthetic gear oil, but catch the oil you drain and let it sit at least over night, check it for metal particules, once again this only applies if the speed at which this is hapening is the same regardless of gear or revs.
Dink

[Anonymous]

It happens at all speeds over75kph in all gears just not under 70

[Dink]

Look very closely at your driveshaft &or wheel bearings.
Dink