Hi,
Recently I have been looking into this topic (V11). My conclusion also is that the plastic holder is not a good solution. Not due to its heat conductivity, but because it makes a proper seating of the tip of the sensor against the cylinder difficult.
But, that also applies to the brass holder. However, the much higher heat conductivity of the brass mitigates the problem that the sensor measures a temperature below the actual values.
A cheap and reliable solution is to apply a bit of heat conducting paste to the tip of the sensor.
As the engine temperature is the single biggest influence on injection, and as the trim curves used by Guzzi vary wildly - I have found 5 different ones - I made my own values based upon measuring AFR over temperature. See attached, AFR stays stable from ~60 to 115°C. The log shows AFR left/right, rpm, TPS and engine temperature.
http://postimg.org/image/osazp82nl/Cheers
Meinolf
