You got stock exhaust?
You're sure you don't have any leaks in the exhaust?
Year model will tell the smart guys what jetting is probably in it.
How many miles on it?

The compression is low enough that you can safely run 87 octane. Any more than that and you are spending too much for absolutely no benefit.

I'll wait until after the dealer warrantee finishes before starting to look the rejetting, although, to be honest, I like the occasional backfire  

I'll do some economy runs to see if there is any real difference between the fuels type which down here are 91, 05 and 98.

The idle fuel adjustment can have some effect on the backfire - but it will not eliminate it.  When you completely close the throttle while shifting or compression braking - the slide drops down and the jet needle completely shuts off the fuel flow through the needle jet.....the only fuel going to the engine is through the idle circuit, and that is not enough to provide fuel to allow the spark plug to ignite the lean mixture.  If you put really big pilot jets in you may reduce the backfiring with the overly rich mixture - but your fuel mileage will suck and the engine will be running too rich when you are cruising at low throttle settings.  Jet your engine for proper running - not for backfire issues.  The TEV valve is supposed to help with this backfire situation when the throttle closes - but maybe because of the E10 fuel it just does not provide for a rich enough mixture.

In order to reduce the backfiring - don't completely close the throttle when you shift or are decelerating.  Hold the throttle just slightly open and the backfire will be reduced significantly.  When you shift gears just slowly roll the throttle off until you have about 1/8th throttle still applied, and then shift....after a while you will get a feel for how to cut down on the noise.  This is not a modern fuel injected engine...you need to learn how to adapt your riding style to suit the quirkyness of the big single with a carb.

And as others have said....make sure you don't have an air leak at the cylinder head or muffler connection.  Don't over tighten the bolts at the cylinder head.....they break easily and should only be snugged up.

First of all, thanks for all of your responses.

So if I'm hearing correctly (especially from Dave and Serowbot), then by adjusting the idle-mix screw mixture (as has been described in the tech area of this website), some of the normal backfiring might be stopped, but not all of it?  (Hope I have this correct).
 
I personally don't care if there is some backfiring, but just interested in finding out if changing the idle-mix flow will help.

I might also ask this: ... By changing the idle-mix mixture, will this also help save the valves from the notorious lean mixture that comes directly from the manufacturer?

Thanks,
Ron G

When my old muffler rotted out I put on a Dyna.  The Dyna is great and I regret not doing it sooner.  Although, I genuinely miss the that big decel "pop".  

My neighbor across the street mentioned he missed it as well.  He said he kinda liked know'in when I was home.  

Best regards,