Hello there jimbo and welcome aboard.

I'd guess you may well be running a little lean with the changes to filter and intake. The cheapest, easiest and quickest way to fix this is probably to consider a Kev fuelling mod...

http://www.xt660.com/showthread.php?t=11641

The Yamaha diagnostic tool Stoic mentions above is not that expensive. I bought one and I have to say it was money well spent, makes setting up/testing/fault finding easy and you can erase fault codes without a trip to the dealer (one saved dealer visit and it pays for itself!) I got mine here...

http://www.cmsnl.com/products/fi-dis...ustomerreviews

Worked out about �100 with tax and shipping.

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