I have trouble getting a handle on this "lean runs hot" concept.  Back in the day, when British twins were all the rage, blue pipes were commonplace.  There was even a product, Blueaway, intended to address this common problem.  The go-to explanation for the cause of the dreaded blues was "your mixture is too lean".  I accepted that as gospel.  I'm a little older now and tend to look into things a bit more.

When I attended Airframe & Powerplant school, we were taught that exhaust gas temperature (EGT) was highest at the ideal stoichiometric air/fuel ratio, about 14:1.  That lesson was reinforced when I was in the air force.  I was a reciprocating engine mechanic.  Our training manuals discussed adjusting fuel mixture using EGT and explained how EGT is highest at the ideal air/fuel ratio.

But I also have real world experience with blued pipes, and a stuck valve or two, that seemed to be the result of lean mixtures.

Every time I see a comment on this forum suggesting that someone's air/fuel ratio is lean because the header pipe is blue, I find myself digging around on the internet in search of an answer to this mystery.  I pretty much always come up with the same answer.  The EGT is hottest at stoichiometric, and gets cooler the further you move away from stoichiometric in either direction (lean or rich).  So I figured I would share the best example I found.  It's clear and easy to understand, and has a nice graph included.  I'm not sayin that the blues aren't the result of a lean, or a rich, mixture.  I'm sayin I don't fully understand the phenomenon.  I figured I would share the info and see what shakes out of the bushes.

This is a quote directly from the Aviation Stack Exchange:

"Exhaust Gas Temperature (EGT) provides pilots a way of monitoring the fuel/air mixture in the engine. It uses the stoichiometric mixture (where Fuel and Air are perfectly balanced so that there is no unburned fuel and no unburned oxygen at the end of the combustion event) as a reference: At this mixture the EGT is at its hottest ("Peak EGT"). Making the mixture richer or leaner will reduce the EGT, and all other mixture settings are described in terms of "Degrees Rich of Peak" or "Degrees Lean of Peak"."

This is a link to their site:

https://aviation.stackexchange.com/questions/21466/what-appears-on-egt-gauge-if-
the-mixture-is-rich-or-lean

Sorry about the link not being active.  If you want to go to the site, you have to copy and paste into your browser.  I'm old and don't have the IT skills that you whippersnappers have.

Finally, I have included a nice graph from Lycomming (aircraft engine manufacturer) that clearly shows the relationship between AFR and EGT.  If you fish around on the web you can also find similar graphs from other manufacturers, like Continental, etc.

I'm curious about your experience with AFR as it relates to your exhaust pipe, cylinder head temp (CHT), stuck exhaust valves, etc.  Regarding the afterglow, I'm with MatchlessG11, my bet would be a catalyst.  If that Dyna muffler has a catalyst the AFR achieved with a carburetor is most likely way too rich for the catalyst.  Rich mixtures cause catalysts to run off-scale hot.  Just a guess.  I know I wouldn't want that goin on in my muffler.  Get it fixed.  

I believe the biggest cause of blue pipes....is folks that are stopped in traffic and idling for extended periods - or even worse yet the folks that warm up their bike before they ride.....or start the bike up in the winter and run it to keep the battery charged and the fuel in the carb fresh.  With no air moving on the outside of  the pipes to cool them - the pipe gets hot enough for the bluing to occur in a very short period of time.....especially if you hold the throttle open a bit to help the engine warm up quickly.

It could be that because lean mixtures burn exhaust valves and spark plug electrodes and can put holes in pistons - that folks believe the engine is running hotter.  What really occurs is the oxygen left over after combustion still has the ability to help things "burn" - and the exhaust valves and spark plugs are the hottest parts of the engine and burn first (and the overly hot spark plug electrode can burn a hole in the piston).  On two stroke bikes the lean mixture can starve the engine for lubricating oil and the piston/cylinder usually seizes.

I start my bike and run it for about 30 seconds....then ride off slowly and avoid full throttle until the engine warms up, and I very seldom have to ride in traffic...........7 years and no bluing on my header.

DragBikeMike wrote on 04/01/19 at 13:21:42:
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OMG...Someone on here who actually thinks about what's going on with their bike instead of just throwing a set of jets because everyone else on here says too.

All very interesting. I pulled the plug on the air fuel mixture screw. I don’t know if I have termed that correctly. I opened it the suggested number of turns from this forum. Because it has been suggested on here that the bike is set up to run very lean. I wonder if I should just turn it back a half turn and see if this doesn’t ease up how hot that catalyst is getting. The catalyst is supposed to get hot if I understand correctly how they work. I just swonder how hot is too hot.

Old school ways with old school technology.
Carbureted engines and spark plug clues are reasonable.
That's not saying you ain't a dinosaur,

That's kinda what I was getting at when I posted my 3/31/19 comment.  Where does this mixture vs pipe blueing tale come from?  The folks at Lycomming, and Pratt & Whitney, and Continental, all aircraft engine manufacturers, certainly have deep corporate knowledge regarding the affect of air/fuel ratio on exhaust gas temperature.  They have all sorts of graphs and operating instructions that state EGT is highest at stoichiometric.  So if the mixture is lean, or if it is rich, the EGT is supposed to be lower.  Why would a lean mixture, or a rich mixture, cause the pipe to blue?  Seems to me, if you have your mixture spot on, the EGT will be highest, and that's where your pipe turns color.  I sort of view my iridescent blue pipe as a badge of courage.  It shows that for a brief moment in my motorcycle's life it actually had an air/fuel ratio that was perfect.