I had an XT660R for a while. I'm not sure if it is the same motor as the Tenere (I assume so) or the same state of tune (not sure), so take this with a pinch of salt:

The 660 motor has plenty of low-down grunt and will pull tree-stumps if the conditions are right. It has a very useful increase in power over the 600. However, there were two issues with mine which I would want to put right before using it for any serious off-roadery.

1. Very poor fuelling just off idle - snatchy and lumpy, as if it went from a closed throttle to half-throttle with no in between. And the kick it gives as the power comes in is pretty impressive. It made wet roundabouts pretty interesting, and riding on a constant throttle (say at a steady 30 in traffic) was a lurching, kangaroo-style affair. Mine was a 2004 model, and I believe Yamaha addressed this with later models via an ECU upgrade. You can alter the CO levels through a combination of button presses on the dash, which helped somewhat, but it can be cured with either a reflash of the ECU (dealer), or a Power Commander and a session on the dyno. There's a lot of info on this on ::.Yam-xt.com.:: Home Page ::.Yamaha XT660X & XT660R Website and Forum.

2. In standard form, the 660R is geared way too high. It is geared for a maximum speed of about 110 mph, which is crazy on a dual-purpose bike. First gear was not low enough for serious nadgery - even slow traffic was a bit dodgy, with a lot of slipping of the clutch necessary. The solution is easy - replace the gearbox sprocket with a 14T item, which brings first nice and low and makes the rest of the gears useable. It has the added fun factor of improving acceleration and wheelie potential. The drawback is that the speedo will now read about 7% fast. Fixable with a speedo healer, if it bothers you. All adds to the cost, though.

As I said, I'm not sure how this applies to the Tenere, or even to later R models, but it may be worth bearing in mind. I liked the bike a lot. I fixed the gearing issue (well worth the few quid it cost) and would have done the others if I had kept the bike. As a long-termer, it would have been worth doing.

Hope this helps.

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2006 XT660R daily ride, 1994 XT600E about to be reborn, Blog: http://goingfastgettingnowhere.blogspot.com/