Major backfire!
 

Hi guys, I have a2014 xt660z, got a k+n air filter and single mtc can. The bike sounds good but I think it's running rich which is surprising me as I thought with the extra air flow it would be lean, maybe I'm confused? Would the fuel mod and O2 mod sort this out? Would snorkel removal/ extra holes in the air box help?

Sounds like you may need to block off the AIS pipe near the airbox.

not doing anything it hasn't always done...
with the MTC pipes you can now hear it..
block the AIS as said...
the AIS lets air into the pipe to burn
un-burnt fuel... thats the poping you can hear..


..

And don't drill extra holes in the air box ! That will bypass the filter.

Removing the snorkel will give it more air (and make sure the air filter opening edge is sealed), but as far as I can gather a too lean setup can also give back firing (loud popping)