I noticed the same problem when I bought a used 2013 3W from Bill Fink.
One cylinder was popping (like it should) the other was huffing... like it was just pumping air.
I tried everything mentioned in this thread. I even bought a leak-down kit to test compression, because, as you know, you can't do a typical compression test.
Long diagnostic story short, the timing belt had obviously skipped a tooth. When I re-installed the belt, it felt like I gained 30 HP. with uniform popping from each cylinder.
I called Bill Fink; did he ever do any engine work on the car? he said No.
I talked to the previous owner, I asked if he had done any work and removed the timing cover? he said No.
I called S&S and asked if it was possible for an engine to leave the factory with bad timing? he said NO! they test run every engine before they ship it.
So, any ideas what happened? From now on, with any unnatural exhaust sounds, I suspect timing.
