You also should check the ACV (decel valve) it adds a little extra fuel under high vacuum situations (like during high rpm/closed throttle) to help reduce decel pops.
You should only need the choke for cold starting.
Hmmmmmm. Sounds like a ton of variables could impact this condition.
Went back to the dealership and asked the tech which pilot jet he put in it. He said he'd only changed the main jet -- and that was changed from a 145 to a 168, as I recall. He remarked that the MJ in the carb was wayyy too small for Colorado.
When I told him that the bike was popping and backfiring on deceleration, he wasn't surprised, He said the problem was likely my FMF pipe. He said that WRs all backfire with low-restriction pipes in Colorado and that it was a basic incompatibility between these free flowing exhaust systems and the carbs on WRs at altitude. Seems like a knowledgable guy, and has been more than willing to answer all my questions, but his explanation seems a bit counter intuitive. When I asked about adding an idle air adjusting knob, he said that they weren't needed, and that he'd adjusted the idle air when he rebuilt the carb.
Now, I am sure this tech has forgotten more about this bike in the last 24 hours than I'll ever know, but everything I've ever learned suggests that popping and backfiring on deceleration are usually associated with a lean condition in the circuit that is in play when the throttle is closed. Going up 3000 feet in elevation (my house -- where I was doing the test riding -- is at 8200 ft and the dealer is at 5300) by my reasoning should make the bike LESS likely to pop and backfire -- because the lean condition is remedied somewhat by the thin air. But I may well be confused.
So now, I am more than a bit flummoxed. Do I chuck the pricey FMF pipe and replace it with an original Yamaha exhaust? Do I pull the carb apart myself and see if re-cleaning the idle circuit does any good? Should I add an external idle air adjusting knob? This shop and tech have an excellent reputation. But I cannot afford to toss a very expensive exhaust system -- only to find out that my problem is not fixed.
Can someone elaborate on the ACV valve a bit? I can recall one on an old Type 1 VW carb I rebuilt years ago, but I don't know anything about them on FCRs.
My goal here is only to make this bike reliable enough to have confidence in -- no matter how far from civilization I happen to be.
At any rate, thanks for all the input.