Racers found a similar issue in the 70's with the old British bikes when they drilled holes in the timing gears to lighten them. Not much performance gain from the reduced weight, but the gears tended to break from the twisting forces as they tried to speed up and slow down with every revolution.

Armen, I'm lovin it.  A little red meat to chew on.  Where can I find the entire article?

"we can compare it with what happens in a real engine, which does not have a heavy flywheel on its camshaft to smooth out its rotation."

Not sure I understand exactly what Mr. Cameron is discussing since I don't have the entire article, but seems to me he's commenting on valve control in an engine with multi cylinders and a long cam shaft.  The bump stick is going through all sorts of gyrations.  The crankshaft is driving the cam and the crank is constantly accelerating and decelerating, faster during power, slower during compression, etc.  The crank is also constantly twisting and unwinding, aggravating the acceleration/deceleration phenomenon.  In conjunction with all the shenanigans that the crank is imparting on the cam, the valve train is also constantly varying the loads and torsional twisting on the cam.  At any given point in cam rotation, some valves are resisting rotation while others are trying to drive the cam forward.  He states that the flywheel in question is "on its camshaft", which implies the test was trying to smooth out cam rotation using stored energy.

If in fact I am correctly guessing at what the article is trying to get across, then I don't think its the reason we lose top speed with the lighter wheel.  We have short bumpsticks and the crank only has one throw.  Neither of those components is twisting up very much.

However, what he is suggesting is something I have been advocating for a while now.  Valve control is essential.  That's why I am not a fan of defeating the pawl assembly in the cam chain tensioner and just letting the plunger stroke in and out every revolution of the camshaft.  You lose control of the valves.  They close on their own and don't follow the cam profile.  Why in the world would you want to give up duration, position the valve at a lower lift for a given crankshaft position, slam valves onto seats, etc.?

I'm sticking with my intial assessment, without the stored energy in the flywheel, the engine starts to lose ground to the wind during the exhaust, intake, and compression strokes.

Aside from the top speed issue, I've been thinking about another flywheel related issue that someone else brought up.  The individual mentioned "improved compression breaking".  I've been doing some research on that but at this point haven't been able to nail it down solid.  Still digging through all my old notes to get some concrete numbers.

Here you see the first set of front brake pads that I changed.  They only had 4600 miles on them.  The friction material is LG (long gone).  I suspect that I did the small flywheel mod (6/14/18) sometime very close to when I changed these brake pads.

Today, I have 20,628 miles on the odo and the pads still have ample friction material.  So I have logged well over 10K miles on the current pads and they got more to give.  I'm guessing the absence of flywheel has something to do with the extended brake pad life.  

The improved brake pad life should help offset any expense associated with the flywheel mod, and you will get quicker acceleration in First through Fourth gear.

Can you shoot us a link to that KC article.  It sounds interesting.

I may be oversimplifying this, and it is only a "thought" and not a theory on why this happens - but it appears the light flywheel allows for faster acceleration in the lower gears as a result of the reduction in the rotating mass..........while limiting the engines ability to overcome the constant load imposed by wind resistance at higher speeds.

This may not be all bad, as I seldom spend anytime with my engine over 4,000 rpm (70 mph with my current gearing).  My 0-60 times were quicker with the lighter flywheel as recorded by the timer on my GPS speedometer.  Since I am not a drag racer and mostly ride 55mph back roads......the lighter flywheel may suit my riding style just fine and improve my engine performance at the speeds I ride.

And I am one of those fellows who has removed the pawl in the cam chain tensioner and installed a spacer to limit the travel.  I cut the spacer to provide the same amount of "clearance" that the stock cam chain tensioner was providing at the time.  So my initial installation provided the same amount of "tension" as stock at the time of installation - there is however no ability for the system to take up slack as the cam chain and cam guides wear.  When I take things apart this winter to do the DR650 clutch modification I will see how much wear has occurred over the last 2 year so riding.

I think Dave has it right. At lower speeds, the lighter flywheel helps the bike pick up revs quicker. Not much HP is needed to run a bike at 30 MPH. When you get closer to 100, HP means a lot. Wind resistance increases as does the square of the velocity. So, many more ponies to accelerate at 90 MPH.
Kevin was talking about torsional vibration leading to all sorts of grief. Part of this is leading to valve float. I wonder if stiffer valve springs would cure some of that? Lighter retainers?
Another possibility is increased vibration at high revs without the damping effect of the heavy flywheel. I friend who got the cam drive on his Airhead BMW sorted out (better chain guides) and found he went down on jetting and got more power. Less vibes might be better metering?
I'm still going with the light flywheel on mine. I spend more time at low revs than winding the nuts off the bike.

"The crank and cam on our single aren't long enough to wind up under torsion."

 This is what I was thinking as well.