The source of that carbon is still on the table...I've tried many solutions...none worked... currently working on an intake temp theory...the valves aren't getting hot enough to burn clean...if I run it hard it won't start hot...but let's not get caught up in this
The reason for the carbon is because of direct injection. With no fuel washing the back of the valves like pre-direct injection, there is no longer anything to keep the valves (and intake manifold runners) clean from the oil vapor from crankcase ventilation that gets pushed back into the air intake. The carbon remnants from the combusion process also adds to this unfortunate side effect of direct injection. This is why so many enthusiast car owners put catch-cans on, to catch that oil going back into the intake. Just look up "carbon cleaning" and you will see what I am talking about if you are not already aware.
For the most part, this is not that big of a deal as a maintenance item as most cars can be done at a shop for $300-$800 depending on the vehicle and motor, but if you have a car like mine (Audi RS7), due to the modern movement of "Hot-V" turbo setups, you can no longer remove enough of the top end due to reverse-flow heads to get to the valves without dropping the engine, so that $300-$800 turns into a $3000+ job.
I do not know what it would take to do a valve cleaning on a Duc motor if you have a lot of miles on your bike. Most cars it is recommended somewhere between 50k-75k miles depending on how you drive. If you drive it hard often, carbon build-up will not be nearly as bad as there is truth to the old "Italian tune-up" method.
Quit overthinking it. Just do what works. Have you never heard “ If it ain’t broke, don’t fix it” ?
I agree with that statement, but as an engineer, I counter it with "But why not make it better?"
On a related note though, I have been doing the same with my Multi. I can easily hear my throttle body move with the bike off, so I just barely open throttle, and I do mean barely, just a touch. If none of you have tried this, try it. Your motor will crank damn near 50% faster and I am not exaggerating since the intake stroke of these big-ass twins do not have to work so hard on the intake stroke to get some air in.
Another thing to consider is moving to a battery that has a lot more CCA. I measured my Yuasa on cold starts frequently and it would often drop to just a touch above 10v when first cranking and gradually increase until it finally fired. This may be because of all the electronics on our more modern bikes, but moving to a Gravity lithum replacement not only saved me a ton of weight high on the bike, but it actually holds full charge at 13.55 (mine does anyway). I have not measured the lowest point when cranking, but it starts on the third crank every single time now vs anywhere from 3-10 with the Yuasa I had in there. That Yuasa, in my unprofessional opinion, is just not enough CCA with all of the electronics that are on bikes these days.
I can hold my new battery with two fingers whereas the Yuasa I needed to hands to comfortably hold it for more than 15 seconds. In full disclosure, part of that reason is because of my small hands while the other and main reason is that Yuasa is just damn heavy!