Topic: rattling when idle is less then 1000

[huili]

I hear this rattling when I first start the bike up but when it warms up it becomes more intermitten and less noticable when I rev it above 2000rpm it goes away I also hear it when I come down from a rev it seems to be comming from the rocker cover does anyone have any ideas. the bike is a 76 cb550

[oldbiker]

If your carbs are out of balance  they will cause a low rev rattle.

[TwoTired]

If your carbs are out of balance they will cause a low rev rattle.

Absolutely true.

The rattle in the CB550 comes from several sources due to changes in crankshaft rotational speeds; the primary chain has no tensioner. As the tension changes from slack side to taught side, a noise is made.  Then there is the clutch plate to basket play that can rattle with the RPM variance.  And, finaly, when the clutch is engaged, all the gearbox backlash shifting to oposite gear faces.  These last two audibly change when the clutch is disengaged.

All this noise in minimized when all four cylinders fire with equal intensity, maintaining the most conistent rotational speed of the crankshaft.

Cheers,

[huili]

thanks a lot guys.  The noise was driving me nuts.  now I know where to start.