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General Category => General Discussion => Topic started by: tris on July 04, 2016, 06:48:08 AM

Title: B11 surging on light throttle settings
Post by: tris on July 04, 2016, 06:48:08 AM

Just need a bit of guidance please chaps!!

The PO of my bike had messed with the sacred screw presumably to resolve (that I discovered to my cost  :angry: :angry:) a poorly Idle control valve

I've got the idle to a nice smooth idle and it pulls like a train at WOT

However at light throttle settings it tends to surge

Is this because I've not got the idle screw dialled back in quite right yet or is it because it tends to sit on the transition between open/closed loop lambda control.

If the latter, will changing the CO trim to "somewhere else" help alleviate this?

While we're on it the rev counter on the bike sits at 1000RPM at idle whilst GuzziDiag shows me 1200 - is this just a case of the rev counter being a bit out of whack for some reason and I should simply rely on the lap top figure?

Title: Re: B11 surging on light throttle settings
Post by: pete roper on July 04, 2016, 11:19:40 AM

Very hard to re-set the screw accurately. I take it you've balanced the TB's and re-calibrated the TPS?

Pete

Title: Re: B11 surging on light throttle settings
Post by: tris on July 05, 2016, 01:01:22 AM

Quote from: pete roper on July 04, 2016, 11:19:40 AM

Very hard to re-set the screw accurately. I take it you've balanced the TB's and re-calibrated the TPS?

Pete

I have Pete - more than once!!

I've also checked the resistance on the oil and air temperature sensors and they're in spec.  Tightened / checked hoses etc - no obvious problems

Are the changes to the sacred screw very subtle? i.e. a very small change can have a big effect?

Title: Re: B11 surging on light throttle settings
Post by: pete roper on July 05, 2016, 06:45:59 AM

Oh yes. Really.

Go to the bay of fleas and pick up an unmolested pair, they aren't hard to find or expensive, mainly because they are either never touched because *Mechanics* are terrified of them or they are right up the shit like yours because Harry Hometune has had a go. Most of them are untouched from the factory. Sure its a gamble, (Don't buy a set where you can't see the sacred screw.) but unless you have a flow bench you're pretty much buggered if the TPS has been re-set since the screw has been messed with.

Pete

Title: Re: B11 surging on light throttle settings
Post by: tris on July 05, 2016, 06:52:15 AM

Mhhh - I'll set up a search PDQ

Thanks for the guidance though

Title: Re: B11 surging on light throttle settings
Post by: ohiorider on July 05, 2016, 08:08:25 AM

I've often wondered why, if the 'sacred screw' isn't to be messed with, the factory doesn't somehow lock it in place permanently once the TBs have been balanced on a flow bench?  Or, since the company is so sticky label crazy, place one close to the sacred screw warning 'DO NOT SCREW WITH THIS SCREW!'

Title: Re: B11 surging on light throttle settings
Post by: tris on July 05, 2016, 08:33:27 AM

 1100 quid every time somebody screws with the screw on after market sales .... or am I being too cynical  :rolleyes: :rolleyes:

Title: Re: B11 surging on light throttle settings
Post by: Dave Swanson on July 05, 2016, 09:08:31 AM

I've been scared to even look at my sacred screw  :laugh:  Where is this screw exactly?

Title: Re: B11 surging on light throttle settings
Post by: ohiorider on July 05, 2016, 05:44:13 PM

Hope pasting this link works.

(http://i115.photobucket.com/albums/n284/bcgilligan/sacred%20screw_zpsmoyo1bn5.jpg) (http://s115.photobucket.com/user/bcgilligan/media/sacred%20screw_zpsmoyo1bn5.jpg.html)

2008 1200 Sport

Bob

Title: Re: B11 surging on light throttle settings
Post by: Dave Swanson on July 05, 2016, 06:10:49 PM

Thanks for posting that Bob!