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Hi guys,
As I'm a newb to GSXR's (and to my GSXR), I wanted to ask this question. My bike's a K2..

When I turn the key on with the run switch on, it does the tach needle sweep and fuel pump charge- you dudes know the drill!

However, towards the end of the fuel pump charge, it makes a rapid, repeating clicking sound. Is this normal- perhaps some sort of purging when fuel pressure is met?
 

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Clicking sounds are generally from sticking relays... Probably your fuel pump relay. Or, it could be from the SET valve/actuator motor. Give a listen and see where the sound is coming from.
 

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It's likely that you're hearing the STVAs cycling. During each startup the ECU calibrates itself by turning the plates fully open until they bang against the upper stop for half a second or so. After that the ECU knows that when the STPS reads such and such the STVs are fully open, so it doesn't keep try to open the STVs past fully open every time you go WOT, simply because it's slightly miscalibrated.

That's my understanding at least; I haven't been able to confirm that from an official source, such as the service manual. Still, every GSXR I've seen up close or on YouTube seems to do it and, if I remember correctly, others here have made the same hypothesis. Anyway, when the plates bang against the upper stops, it makes a rapid clicking sound. Your sound might be something else of course. Try listening to videos on YouTube, to see if other bikes make the same sound, or record one of yours and upload it for us to listen.
 

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Wow, cool explanation.
All of which I miss with my new to me- '97Gixxer.

I kind of feel left out of all this high tech stuff
 

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Wow, cool explanation.
All of which I miss with my new to me- '97Gixxer.

I kind of feel left out of all this high tech stuff
No need to, you have similar technology in your carburettors, the only difference is it's not electronically controlled. It's hard to find concrete data on how the ECU manages the secondaries exactly, but there are, if memory serves, maps in the OEM ECU which map STV opening to TPS output and engine speed. So it's probably control based primarily on those two parameters, although there can be very well be more to it.

In any case (primary) throttle angle and engine speed basically correspond to engine load, hence intake flow rate and intake vacuum and the GSXR's carbs have rubber diaphragms which are sucked by intake vacuum and open and close slides on top of the throttle valves. This, as far as I can tell, serves the same purpose as the STVA and operates in essentially the same way (although with less control over the outcome, so there's some room for jealousy :p).
 
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