thats helpful john thanks

Decat details
 

As mentioned in my advert for my Tenere, I had to remove the catalytic converter from the collector box after it came loose on a long ride. The result was a loud rattling noise at idle and when blipping the throttle, the cat presumably being bashed by exhaust pressure against the dividing wall inside the box and, as pressure subsided, rolling back inside the large diameter tube that houses it.
The obvious solution is to remove the now-useless cat, which may be done as described by others above. Part of the fat tube must be cut back to allow space to remove the cat. This was tack-welded back in place. The cat was bashed smooth on the face that meets the dividing wall, confirming my suspicions above.
I tack-welded the perforated sheet back in place and replaced the rock wool before having the plate welded (using stainless rod).
So the collector is as it was but for the removal of the cat. No extra holes drilled.
As a precaution against lean running I installed a 1k potentiometer in series with the air temp sensor along the lines of the Kev mod (sorry to have to make my own but I was in a hurry) and set it to 0.5k ohms for a test run. By my calculations this should increase fuel flow by about 1.75%. I then checked the plug. The bike was now running significantly too rich, so I lowered the resistance progressively until I now have it at nil (there's still a slight increase due to the baseline resistance of the pot). The plug is fine, perhaps a touch less lean than the old one when changed at service.
Otherwise, the result is as described above: a marginal increase in sound volume but nothing remotely offensive along with an marked improvement in throttle response, especially at the lower end of the rev range. I can stick in a higher gear at lower speeds. No figures on fuel economy yet.
Given that the cat seems prone to breaking loose and then needs to be removed, having it already done seems advantageous to me.
Hope that helps anyone thinking of doing the mod.

Hi mate do you know of anyone who has attempted to removed the Cats from the Akrapovic's supplied by Yamaha for the xt660z?

ive cut mine out about 5 weeks ago

i fitted the kevs fuel mod shortly after ..

i cant find a disernable difference with the fual mod ..but having said that ive only chopped the plug after .. its a nice rusty brown colour so all sems well
the bike is deffo freed up without the cat and is much more flexible and willing to pull low down

i do have a 14 tooth as well but theres no doubt the bike is more flexible and pulls better by far
third will pull from 2k revs ...4th from around 2.3k revs and 5th from around 2.5k revs ..it revs cleaner and pulls harder
with far less fuss and vibration
it eliminates a lot of those caught between gear moments with 30mph being poss in 4th and the low 40s in 5th
for all situations on and off road its much better other than the increased revs on the motorway ..that said a sat nav 75 mph is around 5100 revs
fuel consumption remains frugal and i habnt noticed any increase
all in all its far better than standard and far better than down one tooth on its own ..i can shift between 3 and 4 vibration free ish with clean clean pull which takes me swwetly to 60 plus mph .... it has much more pep and is lovly just to short shift on the torque
top gear just intantly pulls cleand from 47mph on a easy throttle where as before it would just stutter and try and shake itself to peices ..and will pull real urgant from 55mph ..
the combo of the cat and sprocket really wake the bike up ..im delighted with it

... it really is so much better in real world riding /..town off road back road hooning
i can live with a few hundred extra revs on the motorway ... it really is worth the payback the vast majority of the time
thats where i am hope it helps

Thank you for the info...... I'm planning to remove the Cat's from my Yamaha Akrapovic's for the xt660z sometime soon. I haven't decided on Kev's fuel mod or a PCV. How did u remove the Cats? Did u just cut both pipes, removed the Cats, than weld same piece back or did u use a new link pipe?
Thanx JP

ive got to be carful here ....what i can tell you is the bike was run for a short while without the fuel mod and it was fine
its done 1500 miles with it and the spark plug colour is good ....

my cat was just on the standard box ... it seem s a real shame to go to work on 600 quid exhausts .. i hope you figure it

i cant tell you how it was without the fuel mod as i didnt chop the plug but i havnt noticed any difference in the delivery ...

..i found it easier to split the cat housing and prise out the cat ..cutting the rest of the housing after and banging the remaining edges down with a hammer and chisel ..
it messy please wear a mask as allsorts of ****e comes outof the cat when the grinder gets in

http://img14.imageshack.us/img14/2092/img2161q.jpg
By minkyhead at 2011-07-19

http://img838.imageshack.us/img838/8214/img2165m.jpg
By minkyhead at 2011-07-19

Thanx for the info and photo's!!

I read all the thread, but I don't understand if with this mod it's possible to reduce seat's overheating.
I think's yes, but I ask confirm from who make this mod.
Thank's

Yes mate, loads cooler, especially if you drill out the box too!

Drill out the box?
Have you make some new holes in the box, or just make more bigger the existing?

Have you some pictures?
Thanks