What does CO TRIM do?

[dera]

Hi!
What does CO TRIM setting do in our Moto Guzzi? I have MG Quota 1100ES and I can change CO TRIM via guzzidiag, but what does CO TRIM affect to?
I know it affects to a mixture richness but I don't know:
- if it works only in the particular revs? Or on the whole range of revs?
- if it works only for one cylinder? Or for both?
- can it be treated like a way to make a richer or leaner mixture (in the whole range of rev)?

Best Regard,
Michael

[Vasco DG]

Across the whole range. Plus or minus one microsecond of pulse.

[boatdetective]

Mine (for some reason) was set to ten and the bike was running poorly. I dialed it back to 3 (thank you beetle) and my idle improved dramatically.

[redrider]

Idle fuel trim affects the low rpm mixture in the same way as the pilot/idle circuit in a carburetor. Up to about 1/4 throttle, quite a lot, fades away after that.. The range displayed -128 to+127 with 0 being a valid integer. 256 increments. My V11 with Stucci crossover and MIVV cans runs best at +20 or so. Was set at -10 and stumbled and bucked at a steady 3-3500 rpm with Mistrals and stock crossover. A bit worse with the new exhaust setup. Hot days above 90F may need +30 to banish the surge depending on your engine breathing.

[beetle]

CO trim adds a fixed time to the real-time injection pulse-width. This is added across the entire RPM range. A CO trim of +1 adds 10 microseconds to the real-time pulse. A value of +10 adds 100 uS. Conversely, -10 will subtract 100 uS.

The affect appears non-linear because it's is the same amount for any given TPS/RPM value. For example, at idle, the real-time pulse-width may be 2500 uS. If you set CO at +10, the pulse-width becomes 2600 uS. If the pulse-width is 8000 uS at 7000 RPM, the pulse will now become 8100 uS. This is a 4% increase at idle and 2.3% increase at 7000 RPM. Ergo, the affect appears non-linear and has the greater affect at idle.

[Ighani]

So what's the best way to set the trim without a exhaust gas analyzer?

[Wayne Orwig]

So what's the best way to set the trim without a exhaust gas analyzer?

I set it about like a carb idle screw.
Set it a bit too rich. Then lean it out until the idle starts to drop. Richen it back up until the idle speed returns to normal. That is where I stop. For EPA numbers, the setting is going to be a slight RPM drop.

You should be pretty close to zero. I've never run into one yet that benefits from more then a slight tweak.

[beetle]

What Wayne said.

 If you do have an analyser, for the 8V, 5-7% CO, for any 2 valve head, 3-5% CO.

[scra99tch]

On my Jackal it improved the popping on decel at about +10.  On my Quota I don't have a noticeable change in idle speed or performance in a range of -30 to +30.  Which seemed odd to me because when my Jackal was being tuned it started out -16 and did not idle correctly, but bringing it up little by little I could change the idle speed.  As a side note I have my airbleeds turned out on the Jackal about 1/8 of a turn so using CO to set idle seemed to me the next best thing.

[JayDee24ca]

Had the opportunity a week or so ago to have a shop put a gas analyser up the pipe on my 1100 Quota.  Found that the trim was set at +55, pretty high (not that I know anything about it). The mechanic wanted to get it down closer to zero as he said the bike was way to rich and running hot, but found that anything close to zero caused the idle to really suffer. as a compromise he set it at plus 10, but I found that I now have a stumble on low rpm (1800-2800) acceleration.  And it is still running hot. Not sure what my next step should be.
JD

[dera]

To hot means usually to lean, not to rich.
My Quota was also set high - about 70. I set it to 0. But I think it was set to 70 because of the old ignition map (which was very, very lean).

 Ok - thank you for an explanation! Cristal clear :-)

[lazlokovacs]

great knowlege, clearly stated.

Thanks everyone..

[Meinolf]

Hi Beetle,

CO trim adds a fixed time to the real-time injection pulse-width. This is added across the entire RPM range. A CO trim of +1 adds 10 microseconds to the real-time pulse. A value of +10 adds 100 uS. Conversely, -10 will subtract 100 uS.

in addition to above there is a factor applied to the CO value, stored at $B7B3 ($B793 for Quota 1100). Value range is 0-255. $80 is equal to factor 0, $40 corresponds to 0.5 and $C0 to 1.5.

Cheers
Meinolf

[beetle]

Excellent. Thanks Meinolf. I'll check it out.

[Ighani]

What Wayne said.

 If you do have an analyser, for the 8V, 5-7% CO, for any 2 valve head, 3-5% CO.

Why is the reading for the 8V double what it is for the 2V? Wouldn't complete combustion cause the same readings in either engine? And what about the 4V Daytona?

[beetle]

Why is the reading for the 8V double what it is for the 2V?

In a nutshell, because of the different head design.

Wouldn't complete combustion cause the same readings in either engine?

Yes it would. In a perfect world, we should be aiming for 1% CO. The 8V head design necessitates a slightly richer mixture than the 2V.

And what about the 4V Daytona?

No idea. I've never seen one or had any experience with them.