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#1005121 - 02/11/18 10:37 PM CO pot ohm setting  
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Kurt Snyder Offline
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Kurt Snyder  Offline
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I installed a generic pot on my 1995 R1100RSL, aftermarket exhaust, O2 sensor removed. I do not have access to exhaust gas measuring equipment. I don't know if my pot adjusts in the same direction as the BMW pot, but I can measure the resistance. Does anybody know if increasing resistance adds or deletes fuel.

Thanks
Kurt
Northfield VT

#1005122 - 02/11/18 11:12 PM Re: CO pot ohm setting [Re: Kurt Snyder]  
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dirtrider Offline
The Oracle
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Originally Posted by Kurt Snyder
I installed a generic pot on my 1995 R1100RSL, aftermarket exhaust, O2 sensor removed. I do not have access to exhaust gas measuring equipment. I don't know if my pot adjusts in the same direction as the BMW pot, but I can measure the resistance. Does anybody know if increasing resistance adds or deletes fuel.

Thanks
Kurt
Northfield VT



Evening Kurt

I have that info written down somewhere in my shop but have no idea on where. It will be a while before I get back to my shop again & then I have to remember to look for the info. (If I remember correctly highest resistance (lowest voltage output) is rich, & lowest resistance (highest output voltage) is lean as no idle-trim-pot installed = the richest idle)-- But this depends on WHAT side of the trim pot resistor that you are referencing, the 5v side or the low (ground) side.

It's also not the resistance of the trim pot that adds or removes fuel as the trim pot gets a 5volt high input on one end of the resistor, the other end of the resistor is low (ground), the output going to the Motronic is from the 3rd adjustable (wiper) contact sending a higher/or/lower DC voltage to the Motronic. (Motronic reacts to a higher or lower voltage input not a resistance input)

Or, if you are in a hurry you can tell for yourself--- Just start the engine & allow to warm up, then turn your pot screw all the way in one direction (note the idle RPM), now turn the pot screw all the way in the other direction (note the idle RPM). The screw direction that gives the highest idle RPM is the rich direction. (remember the trim-pot only effects idle & j-u-s-t above idle)

Just make darn sure that your generic pot has the wiper contact connected to the correct harness wire. Center wiper to pin #2, low (ground) to pin #1, other end of resistor (5V) to pin #3.


Last edited by dirtrider; 02/12/18 12:04 AM. Reason: added info

D.R. ___
Sent from my rotory dial wall phone!
#1005129 - 02/12/18 02:47 AM Re: CO pot ohm setting [Re: dirtrider]  
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Kurt Snyder Offline
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Kurt Snyder  Offline
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Thank you.

#1005131 - 02/12/18 04:50 AM Re: CO pot ohm setting [Re: Kurt Snyder]  
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Clive Liddell Offline
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Clive Liddell  Offline
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Hi Kurt,

Both my Oilheads have the CO Potentiometer fitted as standard. I originally (in 1996) used a "home" CO tester to check/set the mixture. However, similar to the idle screw on a carburettor, it clearly has a position where idle smoothness is optimum.

Setting slightly "leaner" and the idle becomes uneven.

I set both my bikes very slightly to the "rich" side of the optimum idle and have not touched the setting pot since.

Thanks for your comments D.R. I had no idea what went on beyond the CO pot :>)


Clive Liddell
Pietermaritzburg
South Africa
R850R
R1100RT
#1005143 - 02/12/18 04:11 PM Re: CO pot ohm setting [Re: Kurt Snyder]  
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Kurt Snyder Offline
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Hi Clive,

How did the home CO detector work out? I hadn’t thought of trying that.

#1005150 - 02/12/18 05:04 PM Re: CO pot ohm setting [Re: Kurt Snyder]  
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dirtrider Offline
The Oracle
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Originally Posted by Kurt Snyder
Thank you.



Morning Kurt

A coupe of points to consider.

First, JUST removing the o2 sensor won't make the Motronic 2.2 look for, or use, a Co. idle trim pot. It takes having the correct (or no) CCP in the fuse box (OR, if your early 1100RSL doesn't have a CCP in the fuse box then you need to cut the proper wire in the harness to force full open loop operation)

Second, the Co. setting in the BMW manual is only for (the old) European idle emission compliance. They don't idle or run best at the BMW manual setting as that is too lean for good idle/off-idle operation (Especially with US 10% alcohol gasoline).

Start your idle Co trim pot settings at full rich (should run & idle the best there but will probably idle a bit high). Then ride the bike for a few days, then lean it out about 1 turn, then ride the bike again. Keep leaning it out 1 turn at a time until you notice a degradation in idle & just above idle runability then go back one turn to where it ran best.


D.R. ___
Sent from my rotory dial wall phone!
#1005152 - 02/12/18 05:12 PM Re: CO pot ohm setting [Re: Kurt Snyder]  
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Cap Offline
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Fort Collins, CO
Around here, CO Pot means something completely different...

#1005158 - 02/12/18 06:56 PM Re: CO pot ohm setting [Re: Kurt Snyder]  
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Kurt Snyder Offline
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Dirt rider, I neglected to say the CCP has been removed. Unfortunately it will probably be quite some time before I can ride in VT.
Cap, I hear ya. VT just legalized pot, effective July 1st. As a police officer it’s very frustrating.

#1005193 - 02/13/18 02:53 PM Re: CO pot ohm setting [Re: Kurt Snyder]  
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JamesW Offline
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Florence, Oregon
When I first got my '93 R1100RSL I did cut the jumper in the wiring harness and connected a CO potentiometer which helped smooth the idle but it still had some surging at speed. Then I installed the Innovate Motor Sports LC-2 controller with wideband O2 sensor and all is well. In fact I would say perfect.


James
'93 R1100RSL / '10 FJR1300A
#1005345 - 02/15/18 03:56 PM Re: CO pot ohm setting [Re: Kurt Snyder]  
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Clive Liddell Offline
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Clive Liddell  Offline
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Pietermaritzburg, South Africa
Hi Kurt,

Apologies for the late reply. I need to clarify that the three vehicles discussed here are all non-CAT. If my wife's 2011 VW gives trouble I will have to invest in some expensive test equipment. Just for information - the same folk down in Cape Town that produce the GS-911 also provide testers for cars, including all VWs

I did the CO test around 1996 and I think the cheap home DIY tester was a bit flaky so, as I said, I just got the idle to where it was at its best and that's it.

At the time I also removed the anti tamper seal on my 1991 Mercedes and tried to check CO there as well. There I also ended up getting the best idle and ignoring the inconsistent CO reading. The M-B and the bike setting remain to this day and both are in daily use without further setting.

On my 2000 R1100RT it has been perfect from new and I have not needed to touch CO or, for that matter, the TPI on this bike.


Clive Liddell
Pietermaritzburg
South Africa
R850R
R1100RT
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