strange noise when cold

[huk finn]

I get a strange 'thud" from engine when starting bike from sitting over nite. It happens about 2 seconds after starting. My first thought would be a leaking injector, but that should be a distintive backfire thru exhaust (which it isnt) And that'd happen sooner than 2 seconds of running. The sound is close to a thud. This would be 1 piston-1 knock, if it isnt something getting turned on

I was wondering if it could be a servo turning something on or changing fuel ratio, it is not fans coming on.

So ,, does anyone else get this sound (trying to rule out if its normal normal) .

Bike's been sitting overnite now, I'll go out and see if any rpm drop happens when noise occurs.

Bike is an '06 with around 2500 miles

 

[ionbeam]

It could be the Air Induction (AI) System you are hearing. The system is active when the engine is cold and at idle when warmed up. The ECU triggers a solenoid which opens up an air passage from the air box to four reed valves positioned over the exhaust ports. The AI system remains ON until the engine reaches a specific temperature then the ECU turns the solenoid off. The air injection allows any unburned fuel from the rich 'choke' setting to burn in the exhaust pipes. When the AI is active and you blit the throttle the AI will cause backfiring. You may be hearing the solenoid being turned on by the ECU, you may be hearing noise from the reed valve assembly.

The AI solenoid is under the gas tank, between the air box and the back of the cylinder heads.

 

[huk finn]

by jove , you may have nailed it. I'll try and single out the direction of noise now that I have a clue. I noticed it sounded louder with colder mornings