S4RS Weird throttle slip at slow speeds & engaged clutch

[itsmebanky]

Still trying to identify the issue of this weird problem I'm having - at very slow speeds, usually with the clutch lever pulled in, occasionally, the throttle grip will slip ever so slightly, as if it misses a click. The feeling is felt in the throttle grip and when it happens no acceleration occurs. I've stalled the bike a few times because as I was accelerating to take off, this weird slip thing would happen as I release the clutch as i would expect - then it dies. After the slip, it will throttle and accelerate as usual, as if it did not miss a beat. There is no over rev for compensation of the missed throttle input - it just revs normally.

Any ideas on this?

Bike: 2007 S4RS

[Dirty Duc]

What kind of grips?

[Bill in OKC]

Do you only notice it as you are taking off?  It almost sounds like a clutch issue.

[itsmebanky]

stock grips

yes, its usually when i need to take off either from a dead stop or from a really slow roll. almost always when im feathering the clutch but will happen when i'm not on the clutch either..

[Bill in OKC]

When my bike was brand new I had an odd clutch problem.  Not so much when taking off but when cranking on the throttle.  A sound like a spring unwinding and some hesitation.  My clutch was slipping.  I replaced my clutch springs and the problem went away.  Another time after installing a different clutch, I had some problems with odd grabbing/releasing when taking off.  It was an issue with the clutch pack.   Try this - when the bike is not running, try opening and closing the throttle and listen/feel for the click.  If it doesn't happen when the bike is off then it might be elsewhere.

[Speeddog]

Does it make a 'kuunk' sound when it happens?

If it does, it's a light backfire through the intake.
The air going out opens the butterfly, so you feel the throttle go slack.
Flipping the butterfly open that quickly, it pulls a bunch of air and goes so lean it dies.

Generally due to being too lean at idle or valve clearances out of spec.

[Bill in OKC]

Yes, that sounds good.  Here in OK we can get regular gas and e10.  On my Aprilia when I used to get e10 sometimes, the bike would miss a beat very now and then.  My S4rs would act similarly -e10 or regular- with the stock ecu, it was just too lean.