SOHC.co.uk Forums > CB500/550

CB 550K3 suddenly running very lean

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Ashdowner:
Bought my CB550K3 and it unbelievably had 3 different grades of NGK plug in it - DE7EA, DR8ES and DR8EA. Now has the recommended DR7ES but is running incredibly lean, with the plugs almost white. Do I need to increase the jet size or raise the needle and what is the difference in those two options?

deltarider:
First things first. Sufficient fuelflow? Floatlevels OK? Original airbox and airfilter? Any airleaks?
On the K3s the idle jets are notorious for clogging. Wouldn't touch the needles.

Ashdowner:
Floatlevels were done a month ago and had the carbs ultrasonic cleaned at the same time. Idle has always been poor but up till yesterday it was fantastic above 4000rpm with beautiful brown plugs. Now they're grey/white

Bryanj:
I would suggest removing the push in pilot jets

Ashdowner:
Gulp. That seems a bit drastic, and that's only affecting the idle. It's over 4000 rpm that it's running lean and that's on the needle jet

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