Tuning with the potentiometer

[ColinFromDevon]

Wondering if you guys know about using the potentiometer for tuning? this is not what BMW put it there for by the way, but I've fiddled with it extensively and have it set so my bike runs quite rich, and wow does it fly ! especially powerful at low revs, kinda brings the whole power range down to lower revs and condenses it. To be honest I wouldn't ride an R1100R if it was standard as I find the power/accellaration a little too lame. Down side of doing this tho is that it runs a bit jumpy in 1st & 2nd gear at low revs (cos it just wants to leap off with even a little throttle opening) but if you don't live in a city then I think it's well worth it for thr lush extra torque and power achieved at low rev/midrange. Discovered this by accident after my BMW dealer was trying to eliminate the backfire my bike sometimes has, they made it leaner and killed it's performance (and it still backfired sometimes) so after finding out what they had done I endeavered to get the performance back, and then improved it to a place I'm very happy with. MPG is around 45, up to 55 on long runs, the throttle is really responsive!

[Ton1959]

So what did you set the mixture too.

[Caerleon]

Hi Ton,

I have a 1100RT-P without Cat, so mine has a tuning pot fitted also. I have been having issues with low speed control as the throttle was like supersonic as soon as it was opened a little bit. I looked at all the base settings like the TPS voltage and the CO output.

The pot is a simple potentiometer, but you have to turn it alot to get it to move, wait for it to settle then measure. What i have found out is that the Police had the TPS set at .400mv and the CO measured 6.5%! This is why it was running really rich, i am guessing this was a requirement to eliminate the surging issue, which of course it never exhibited being over rich.

I decided to set the TPS back to factory setting of .385mv, but at sea level I understand it should be .390mv and the CO 1.5% - it ran really smoothly, but then i noticed a idle issue with misfiring. This i put down to carbon deposits built up in the combustion chamber.

If you disconnect the CO pot and pull the motronic fuse it sets it to a base level of CO 1.8%. Personally, if you have been running lean before, you can turn the CO up till you notice that its running rich and then lean it a little - if you can gauge by ear, you should get near to ideal without a CO meter. Dont mess with the TPS unless you have issues with idling - seriously its not worth it!

[Ton1959]

I have it just over 1,5 % Co and it is running okay. I used a carbtune and NGK iridium spark plugs. And my bike is doing well on petrol too

[ColinFromDevon]

This is different to TPS. The potentiometer just adjusts fuel mixture, and I think maybe just for lower rev range. BMW have them set lean for emissions control/ smoothness and MPG etc, but they put it there so they could set it right for different countries regulations etc, but generally too lean, which is general consencus. The potentiometer I'm refering to is located under the plastic side panel just below the saddle on the right hand side of the bike (R1100R). You have to lie on the floor and look up to try see it, what there is to see is a copper coloured slit/screw set in a rubber cup. Anti clockwise makes it richer. I maybe went out 2 or 3 whole turns eventually ? by little increments, I'd recommend a 1/4 turn at a time until you notice it begin to change the performance then do smaller turns , keep going til you like it. If you go too far it starts again at the opporsite end of the spectrum. I found the sweet spot was pretty close to the max rich end, here the amount of change for a little bit of turn increases a lot, just a 1/64 of a turn makes a noticeable difference. Bike was so responsive, great ! But then I'd realise that I'd lost smoothness and that the bike was a bit more grindy and would have to change gear early to avoid vibration. So 'd turn it back down a bit, but then I'd miss the feeling of opening the throttle a bit in 2nd gear at low revs and the bike just instantly fly forward, I would tune it up again. So I went back n forth for months n months, eventually I realised that I loved the good instant performance and that it gave me much pleasure, and that I just had to pay the price of less smoothness. By the way, sold that bike now and have moved to a R1500R, which is a whole different beast to tune, what with closed loop system. Getting there though.