IMO, Harley has been trying to keep a dieing ship afloat for 20 yrs. They have struggled valiantly to comply to sometimes ridiculous EPA regs in an effort to keep the antiquated Vtwin engine design alive.
From the Evolution on I've seen and heard complaints of excess heat.
AIR COOLED engines require far different setup than a liquid cooled engine, and there are limits that cannot be exceeded without producing excess heat, drivabilty, and durability issues.
The problems, IMO have been made worse by Harleys attempts to meet the new regs with Fuel Injection, by a continuous regime of building leaner running engines.
Air cooled engines require a richer mixture to help control the heat. I've seen Dyno runs that showed a stock FI Harley running at 16 to 1 at idle and still 14.8 to 1 at full throttle. The real combo should be somewhere near 13/1.
This all aggravated by the new "clean burn fuels" with corn liquour, which actually leans the mixture even more because of its inefficiency.
Harley Davidson could have and should have spent their time designing a water cooled version, now they are caught in the middle with an engine system that cannot meet the regs without major mods. Since Harley is required to meet the regs first, its left up to us to make the changes (break the laws) to obtain an engine that doesn't melt your socks!
Most of the other brands have used the liquid cooling and meet the laws. Harley fell short again in not moving with the times and seeking the almighty profit. JMO FWIW twinotter