Hi, I browsed this forum before making my current purchase of a 2006 X model with 17000ks on it, and as I have further questions I thought I should sign up.

I was wondering how I can tell if there are any mods on it. The previous owner added some fog lights and a custom seat, so it's possible he tinkered with the internals. What would I look for?
(I have no mechanical knowledge, so simple words and descriptions please.)

If the sprockets are changed up or down, does that throw off the speedo/odo?
What's the easiest way to tell if the speed indicated has been corrected or has the 10% error (*without* getting a fine or loss of licence)?
If the speedo has been corrected, would my odo be off?

My riding terrain is the hilly back-roads of mullum-lismore-murwullimbah, etc.
My previous bike was a drz400, on which I averaged 23km/l, and I was told to expect better efficiency from a fuel injection bike even with the bigger engine.
However, my first two fill-ups averaged out to a 19km/l consumption.
It's probably because I was used to the higher-revving drz and was staying in 3rd too long, and taking some of the sharper corners in 2nd. I hardly used the 5th gear at all (except for that bit where I get to see how fast I can go before I run out of straight road - 157 *indicated* so far).

However, I tried using higher gears and lower revs through curves and today I got 24/l.
Is that good or can I do better?

What are the average workable speed ranges for the gears for this model (assuming no mods)?
eg, is 3rd okay to pull from 40km,
is 4th lugging if it pulls from 70km?

I'm a bit worried about lugging the engine, and I kind of do like being in a gear that will respond to input immediately coming out of the corner so I can punch through it. In a higher gear there is always a bit of delay before the engine really accelerates and it sometimes feels 'spongy'.
However in a lower gear there is the problem of the bike being a little twitchy as the engine-breaking/acceleration fight it out. I can use the clutch to smooth that out a bit, but it's a bad habit I'm told.


There is quite a bit of popping going on whenever I back off the throttle - does this mean I'm wasting a lot of fuel and is it because the settings are richer or that it may have been modded? Or is it an EFI thing?
It seems loud, is that normal for this model? I don't want to be obnoxious, I like a bit of noise but not too much. If I could get rid of the popping I would feel less self conscious. The dealer replaced the baffles, so it's not that.

There apparently is a way to change the fuel/air mixture via the dashboard - is that worth tinkering with?
What's the basic principle?
eg, more fuel = ? vs. more air = ?
And how does this differ from the fuel mods that are available?
Is there a mod for better fuel efficiency, or just more power?

Is flash-lube still a good thing to be using when I fill up?

Apart from oil, chain lube and tyres, do I need to be concerned about anything else? I just want it to go as long as it can without specialist intervention.
I used to change oil every 1500 on the drz, is 3000 or 5000 the interval for the xt?

It's a bit buzzy and vibey, but I am used to that with the drz. The vibes are just a bit *thumpier* this time.

I am enjoying my arse off with it, it's a step-up in terms of bike skill as I can take corners faster and with more lean than I could the drz.
It's noticeably more sensitive to bumps and so on in those corners though.
I've only been riding a couple years and am still on P's.
I'm thinking of doing an advanced learners course to keep myself earthed, as it makes me feel more risky and feel like I'm better than I am.

Firstly, to XT660.com

What a lot of questions you have!

I�ll see if I can answer some�

It is unlikely that any internal engine mods have been carried out (big bore, camshafts etc.) Not many XTs do. The most likely mods will have been done to the intake and fuelling.

The fitment of a Power Commander will be obvious because you�ll see it under the seat. If it has a fuelling mod such as a Kev Mod, then again, you�ll find a dial somewhere under the seat. It may have a K&N or DNA air filter, which can be checked by looking inside the airbox.

The airbox may have been drilled (you will see 5 holes in the airbox) and the snorkel me have been removed.

Suspension mods, such as a change of dog bone length or shock will be visually apparent. If different fork sprinks or fork spacers have been fitted, you�ll have to take the tops off and check inside.

A sprocket change will throw the speedo and odometer out. If the speedo has been corrected you will find a speedo healer box (or similar) fitted under the seat. If the speedo has been corrected the odometer will be out. In stock trim the speedo will read 8-10% high, but the odometer will be pretty much accurate, maybe at most 1% out. The only way to check speedo accuracy is to check with a GPS, or a speed app on a smart phone.

Sounds about right.

All the above can be improved a great deal with the various fuelling mods available, such as a Kev Mod, Power Commander etc. Also carrying out the twist grip mod, cush drive/hub mod and will help a lot with improving surging and low down tractability.

Kev Mod

Twist Grip Mod

Cush Drive Mod

Popping on the overrun is normal, it is the AIS (part of the emission control system) doing its job and cleaning up any unburnt fuel in the exhaust system. It has no effect on the running/fuelling of the bike � you are not wasting fuel.

The popping can be significantly reduced if you block the AIS pipe.

AIS Mod

Adjusting the CO at the dash only influences very small throttle openings, it may help with surging, but won�t make any real difference to power/economy. Adjusting the CO is not the same as fitting a fuel mod (as mentioned earlier). A fuel mod will adjust the air/fuel ratio across all throttle openings on a bike like the 06 XTX without an 02 sensor.

A Kev Mod for example will improve the efficiency of the engine/fuelling. Whether that extra efficiency is turned into power or economy depends on how you use the throttle!

Adjusting CO

I assume that�s a fuel injector cleaner/fuel conditioner? If it is, then it�s a good idea to give the bike a shot now and again.

Main things to watch that will/could cost you money in the future are steering head bearings, swingarm pivot and suspension linkage lubrication. Check for unusual knocking noises from the right hand side of the engine, which could be a loose crank nut. Other than that all the usual stuff.

Change the oil every 3K miles (5K Km) using a good semi-synthetic, renew the filter every other change and you�ll be fine.

Joining the XT Supporter�s scheme is a good idea too � gives you access to a load more technical information and support, plus much more. Find out about it here.

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Thanks very much, I'll read up on those things.
I never noticed anything under the seat, so I must be mod-free.
I'll need to get to know the bike more before I decide if it needs to be improved.
That crank nut thing - is that preventable by tightening is or is an internal failure that I can't do anything about?
(yes, I don't know what a crank nut is).