Hi, I'm a long time member of the forum and proud owner of a 2004 xt660x, and i'm writing from Italy.
During last year I've tried many possible solutions to minimize the typical on-off problem of this bike.

These experiments just ended with a new type of fuel mod that i think could be interesting for the community.
The main problem with the classic fuel-mode obtained adding a trimmer ins series with the NTC is that the correction is not linear due to the non linear behavior of the NTC.

In fact for instance a 1kOhm correction changes the temperature read by the ECU by ,more or less 5�C when the real temperature is 10�C and by over 20�C when the real temperature is 40�.
This causes an engine behavior that's changes together with the outer temperature.
It would be much better to have a linear correction over all the temperature range.

This is possible by adding another NTC in place of the trimmer.
To guess the correct value of this NTC you can simply:
- measure the resistance of the original NTC @ 25 �C (1.9Kohm fom me)
- found the optimal correction (in Degrees) that allows your bike to run smooth (form me is around -5�C)
- put a resistance or set the trimmer to obtain that correction (around 500 ohm for me)
- Buy a NTC with the correct resistance @25�C (i've bought a 470Ohm @ 25�C NTC)
- Put the NTC in series with the original one and put it on the air flow (another hole in the snorkel?)

That's all.

This type of mod is not comparable to a system like a power commander, but works much better than a single trimmer for me.
I'm sorry if my english is not so good but i hope my explanation will be understandable and useful for you too.

Gabriele