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Why do some Buells run rough?
https://www.ukbeg.com/forum/viewtopic.php?f=7&t=4388		 Page 1 of 9
Author:  pash [ 13 Jan 2010 07:34 ]
Post subject:  Why do some Buells run rough?
A topic to promote discussion...

I have been thinking about the Buell lumpiness issues that pop up from time to time and why don't they affect all Buells? Firstly, it is down to rider perception. If your expectation of a Buell is something rough and ready, then you are less likely to think there is a problem if indeed there is one.

But what about standard bikes which are lumpy part throttle, or don't shut down quickly to idle? Sure you can remap, but why should you have to?

I know that not all bikes are like this, for example:
* I have ridden a standard 08/09 Uly which was very smooth, with smooth pickup from idle
* I have ridden a standard 07 Firebolt that was quite smooth (smoother than mine when new)
* I have ridden a Micron equipped 07 Firebolt that was quite rough part throttle* I have ridden a standard 08 12S which was smooth (but gutless)
* I have ridden a Micron equipped XB12Scg which was OK, but did not shut off particularly quickly

So, why are they lumpy part throttle, especially as they are in closed loop control? If we take a step back, I don't think production tolerances on mechanical parts, such as cams, valves etc. are likely to make a difference.

This leaves ignition and fuel flow. The static timing is easy to check and I would say that the engine is probably quite insensitive to changes in ignition timing of 1 or 2 degrees. Better engine earthing has been recorded to help.

If we think about fuelling, it is delivered as a function of engine speed and TPS. Corrections are then applied for IAT and CLT (and pressure for 1125 models - and maybe 2010 XBs). The closed loop area of the map, with the corrections applied is then finally corrected by the O2 sensor output to stoichiometric. If you disconnect the O2 sensor, you tend to end up with a smoother running bike, but that is defeating the object of the sensor...

I have emailed Bosch and asked for the lambda sensor error, but I think this is immaterial as I believe it is the closed loop area that causes the raggedness, where the fuel flow is so very different to stoichiometric, that the corrections are very large, and hence any overshoots are large.

With a little knowledge of how the system works, you can discount the CLT as, when the engine is warm, this is more or less 100% over a wide temperature range. From the Bosch catalogue, for a similar sensor, the tolerance in measurement is 5%, resulting in a max error of 10 deg C, or 0.6% difference in fuel flow, so not much of an effect.

For the IAT, the ECM increases fuel by approximately 10% every 25 deg C. From the Bosch catalogue, for a similar sensor, the tolerance in measurement is 5%, and therefore the error in fuel flow is likely to be 2 deg C at 40 deg C and hence around a 1% change in fuel flow.

I would think speed measurement is not an issue as you would see fluctuations on the rev counter and since the speed is measured from the CPS, you would have problems with ignition also.

So, the fingers point to the TPS. Sure, you can set the TPS, but what else could be the issue? Slack in the linkage is one (hence hard TPS reset) or maybe non-linearity in the signal.

This is primarily aimed at XBs, but I bet some X1s are lumpy too, after all, why would someone go to the trouble of putting a Mikuni on one?
Author:  Devonbob [ 13 Jan 2010 11:02 ]
Post subject:  Re: Why do some Buells run rough?
A well reasoned argument Pash. :yup:
Author:  Maz [ 13 Jan 2010 11:10 ]
Post subject:  Re: Why do some Buells run rough?
Pash, YHPM ;)
Author:  edd [ 13 Jan 2010 12:05 ]
Post subject:  Re: Why do some Buells run rough?
I've ridden several pre 'cat' XBs of most types except the Uly. They all ran smoothly once warm, so I couldn't say. :?

Only Buell that didn't was a demo X1, who's CDI unit would hiccup at low revs on roundabouts......preferred the good old Cyclone anyway! lOl
Author:  coppersaucepipe [ 13 Jan 2010 12:58 ]
Post subject:  Re: Why do some Buells run rough?
Wife's 09 Scg is very lumpy at tickover but feels as smooth as any other bike I've ever ridden once your moving faster than walking pace. I put it down to the fact the bike has a tractor engine in it and was just a feature of the bike. Are they not supposed to be that lumpy at tickover?
Author:  Mitch [ 13 Jan 2010 15:39 ]
Post subject:  Re: Why do some Buells run rough?
my 07 xb12, 16500 miles on it, has been fine, even better since i did the TPS hard reset, which made it run much smoother at low revs. only mods to engine are a pipercross air filter, and breather mod.
the idle does 'hang' sometimes, but usually after a fast run on a hot day, any other time its ok.
Author:  Ash [ 13 Jan 2010 16:27 ]
Post subject:  Re: Why do some Buells run rough?
Somedays mine is smooth with a sharp responsive throttle, other days it feels laboured, very viby and as if it cant be arsed ... I put it down to if the planets are in line or not, cant work out what else it can be!
Author:  Bonzo [ 13 Jan 2010 16:35 ]
Post subject:  Re: Why do some Buells run rough?
Ash wrote:
Somedays mine is smooth with a sharp responsive throttle, other days it feels laboured, very viby and as if it cant be arsed ... I put it down to if the planets are in line or not, cant work out what else it can be!


Both my M2, and to a lesser extent my XB are like that. I think it's to do with humidity levels, definitely better on a cool, damp morning. Also, I have noticed (again on both bikes) that if I stop, for instance to fuel up, about 5 minutes after setting off, that the bike feels smoother. I suppose this can be partially explained by the full tank having a dampening effect, but it's noticeable even if I haven't filled up :?
Author:  Ash [ 13 Jan 2010 16:49 ]
Post subject:  Re: Why do some Buells run rough?
A few miles before I need to fill up, it miss behaves a lot, with really loud popping, banging and the occasional hint of a blue flame out of each pipe, once I fill up it is a lot less again
Author:  Bonzo [ 13 Jan 2010 17:00 ]
Post subject:  Re: Why do some Buells run rough?
The good thing though, unlike most bikes I've owned, is that the faster you go the smoother it gets. So I just go as fast as I can :P
Author:  pash [ 13 Jan 2010 19:53 ]
Post subject:  Re: Why do some Buells run rough?
So I had a chat with a number of people offline and it appears that the 08/09/10 bikes are a little hit and miss, some good, some bad. Changing the TPS appears does not appear to change the situation, however changing the throttle assembly itself does appear to yield good, if not variable, results.

Indeed, there are rumours of Buell witholding European stock at warehouse and changing throttle bodies over on the quiet.

Anyway, out of interest, can anyone send me a log of their bike ticking over, be sure to tell me what model it is...

Cheers

Nick
Author:  Markj [ 13 Jan 2010 21:28 ]
Post subject:  Re: Why do some Buells run rough?
Manufacturing standards are shit? I mean were (wonder why). :oops:
Author:  supremesoundz [ 13 Jan 2010 22:06 ]
Post subject:  Re: Why do some Buells run rough?
this poor running seems to be popping up alot! my xb12scg 08 seems lumpy and not as gruntt as id imagine, of should i say wheelie happy i rekon..... maybe once this is cleared as to, whats wrong, whats not, what should be adjusted or not....... we should all have a uk buell enthusiasts tuning weekender, to get all member buells sweet as a nut :clap:
Author:  THE FLYING DUCHMAN [ 14 Jan 2010 00:33 ]
Post subject:  Re: Why do some Buells run rough?
Well first off IMO.

The XB engine needs 4k min to run in. I also think that the DTFI-2 and maybe even the DTFI-3 takes much longer to adjust to varied temps etc than other injection bikes. The TPS and idle revs, IMO on the XB, must be a perfect set-up otherwise you get throttle roll-off lag and/or bad low rev control.

Regards your question Pash. I think some of the problems people have are a combination of many things.
Author:  Motorrad [ 14 Jan 2010 02:16 ]
Post subject:  Re: Why do some Buells run rough?
pash wrote:
But what about standard bikes which are lumpy part throttle, or don't shut down quickly to idle? Sure you can remap, but why should you have to?

Some aspects of the maps seem set up to satisfy emissions reg's (EPA in the USA), rather than for optimum performance. Just as re-routing the breathers is done to circumvent a setup that was made to help emissions and not for performance, perhaps it is "normal" to expect to fiddle with the fuel and/or timing maps to create a smooth, yet slightly "emissions be damned" bike.
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