Some wierd knucking noise

It only happens on the cold engine and only couple of times. There is a distinct knock like within first minute as bike starts. It has roughly 2.5k and I think it started in the last couple of weeks.

It goes away as and I do not hear it until I try to start the bike next day or during lunch on the cold engine.

Yes, did the search.

I'd like to help. But first, what does a knucking noise sound like? :glare:

Is it kind of a Three Stooges "Nyuck nyuck nyck" sound? If that's what it is, then try two fingers in the headlights.

Yes, this is fairly normal.

It's been discussed before but I don't recall exactly what it is.

Part of the warm up process something opens when the exhaust gets hot enough, part of the emissions or something like that if I recall correctly.

Maybe the 'knucking' noise wouldn't be so obvious if you'd stop eating lunch on your cold engine!

Sorry, I am an engineer. Couldn't help myself after reading the Three Stooges comment!

Also known as "lean pop". It's a lean misfire, gas puddles until the intake tract warms enough to promote vaporization. The misfire creates a dead cylinder, and the momentary mis-balance is part of what you hear and feel. Especially prevalent as the ecm starts leaning out the initial cold start enrichment, say, about one minute into the warm-up.

Rad, that is about right. So, nothing to worry about?

Thanks guys.

Oh, and it's another little item the PCIII cures. Is there anything it can't do?

Maybe the same think I hear on my '05 FJR. I just got it new from dealer (heldover) and have had it out twice for a total of 178kms. Both times when first leaving my driveway have heard 'rattling' noises from bike but only when lightly accelerating and then its gone. I do let bike idle for a minute while putting on helmet/gear to warm up. Both times it surprised me but kinda thinking it has to do with fuel mgmt.

Haven't heard it any other time when riding or even when stopped for an hour (showing bike to friends ) and starting off again. I'm gonna be aware next time and track under what circumstances it happens.

Well at least I know what to call it now. Pretty typical IIRC. It has been discussed a while ago. My bike's been doing it since new, about 20,000 miles. Only when cold, only a couple times in the first minute or two when started, etc, etc. Thanks Rad for the technical explanation. I'll stick with 'knucking'