Originally Posted by JMo (Post 114584)

Hi Jami - from what I understand, the O2 sensor only works on the part throttle opening (that is up to about 18% - so off-idle and low revs) to make constant fueling adjustments... once the engine revs higher than that, the main EFi unit takes over (in your case adjusted by the PCV).

If the O2 sensor is still fitted, then at lower engine speeds it will try and send a signal to the ECU, possibly conflicting with what the PCV is trying to tell it... by removing the O2 sensor (and fitting an eliminator), all you get is the PCV map the whole time.

I'm not sure it will result in any more power necessarily (I don't imagine so), only that the power curve will be smoother and not 'interrupted' at all, as it is only using the map in the PCV... I doubt you'd have to remap the PCV again, unless you were being really fussy!

I imagine Kev is your man to really explain the technical aspect of it...

J xx

Originally Posted by Jami (Post 114586)

Thanks for the answer JMo! Well explained. I'm happy with the top and midrange power. I would just like it to work better on revs below 3000 so that just might be the answer.

I wasn't around when the bike was being dynoed and tuned up but I trust the guy who did it. But still I'm wondering why it backfires so much on lower revs if it's now properly set up. Is it just typical for the type of engine or is it the O2 sensor still confusing it?

And no, I'm not a fussy type of person, just practical :-).

Kev, if you're reading this, I would indeed like to know more about the technical aspect of the O2 sensor/eliminator. Thanks.

Jami

Originally Posted by JMo (Post 114587)

I think the back-fire/overrun popping is more to do with the AIS system - I presume you still have that fitted, or have you blocked it removed it?

However, you could be right that the O2 sensor is sending a signal to the ECU which is trying to lean the engine right off on the closed throttle - I imagine removing the O2 sensor will certainly help, if not eradicate that trait completely... it should certainly sort out any fluffiness you've got below 3000rpm...

As for blocking/removing the AIS plumbing, it is very simple to do, and certainly minimises that overrun popping... there is some info on here about how to block it effectively, but to be honest, I'd just junk the whole set up and block the inlet to the exhaust manifold with a plate (don't forget to seal the airbox hole too though!) - in fact I understand Petebog is planning on producing a kit to do this, but it is pretty easy to do yourself...

xxx

Originally Posted by Jami (Post 114610)

Yes, I still have the AIS system fitted. I just searched the forum to find out what it is - I wasn't aware of it before. So much information here.. That seems to be the real reason for backfiring. I'm about to take the tank off anyway (got some wiring to do and I wanna make it neat) in near future so while at it I might as well remove the whole system. So will it cause an ECU fault code or not?

Thanks again!

Jami

Originally Posted by Kev (Post 114619)

Another way.

http://www.xt660.com/showthread.php?p=101266&posted=1#post101266

If a bike is run on the dyno with the AIS open, the air/fuel ratio will be out & the fuel map will be made wrong. The AIS must be blocked off before the bike is run on the dyno.

Originally Posted by Jami (Post 114627)

Damn. I was afraid of this. I wish I had known about it before taking it to the dyno. Any ideas how much 'wrong' the map is? Perhaps I could try adjusting the map by myself. I paid 250 euros for the dyno run and tune-up and I'm not gonna pay that again. It can't be that much off since the engine feels and sounds right.

So it's running too rich now? Did I understand correctly?

Jami

Originally Posted by Kev (Post 114656)

The AIS injects fresh air into the exhaust at any time, depending on the throttle position & RPM, so it would be impossible to know where to adjust the fuel map manually. Any good dyno tuner should know about the AIS, as it has been around for years & most bikes have these days.

The extra air that is injected into the exhaust shows up as a leaner mixture then it really is, so the dyno tuner runs the fuel map richer to correct this leaner A/F. With the AIS blocked off the exhaust gas readings are now a true refection on the A/F ratio.

Originally Posted by Jami (Post 114795)

I called to the mechanic who did the tune-up and asked him about it and he said that he did block the AIS before tuning so no problem there. I just didn't know about it. Thanks for the info.

Jami