I ran mine on a beach for a short squirt using the 172 main. It ripped.

If you're worried, sacrifice a new plug. Do a 5 second WOT pull in 4th gear walking pace up a slight incline. Tear it out and then go home and cut the threads off to check for the black line around the base. I think you'll be plenty safe. IMO this needle if anything feels a touch lean at constant throttle just before it comes onto the pipe. Great off the bottom and great up top. It could also just be the bike preparing to cut loose.

To the OP, I can appreciate your concern and ultimately I doubt any text will make you feel comfortable, but here is my experience on extended top end.

I have nearly 3 decades on an 200cc yamaha IT, it is on it's third bore size, original jug, original rod, original big end. The hours on this engine are uncalculatable 1000's? I have never broke a skirt, gouged a jug, rattled a little end, honestly, the bike has never fouled a plug, I put a new plug in it at the start of each season after my winter freshen up and never look at it again for the season, the jetting is clean. This engine works its butt off running with the big bikes of today and yesterday, it has never left me wanting in any condition but running the sand down in SC where the big bores just out power it on the top end. I cannot find my original manual , so I've lost decades of numbers, specs and such,(sore subject, new shop, wife had it last, she admits it, no idea where she put it a few years back when we were moving stuff) but I know sometime in the 90's pretty sure early 90s I changed to Motul 800. I'm not saying buy Motul, keep reading.

I mix my gas 50/1 since that change from the Yamaha lube I used for the first years of the bike, pretty sure original spec was 24 or 32 to one. When I go riding where I expect some extended high rpm runs, I mix 40/1, that is the extent of my prepping my bike for that. That little engine is air cooled, yours is water, it spins with a hell of an overrev it lives its life likely 30% higher rpm than your bike at any given moment. When I run sand I'm running with a TT500, an XT600, a 426 and a kx250 the bike may run for 3-4 hours without ever shutting off it may be pinned wide open for durations that I still wonder why it doesn't just die.

The bottom line, if your plug has a good color print under your normal riding conditions, and you need a little more info, do some WOT pulls from 3-8k as Jakobi mentioned, but I suspect you'll see good color. If you want some mental assurance, run a tank of 40/1 during that race and have a great time!!!!

Thanks for the input. I will do a plug check on a new plug just as suggested.

The story of your IT200 was great to read. I rode one back in the 80's and to this day that is the bike I loved most. Finished the Barstow to Veges in '88 on one. Not the dual sport ride, but the real deal.
Man, I loved that bike.

I'd be super interested in seeing a pic if you chop it like that too Ando!

FWW Bailey28 used to run a 42 NOZH 160 in similar elevation and temps to me. I called him mad as its the equivalent of us running a 162. He swore the bike absolutely ripped, and put countless hours on it until he had a nasty off and then sold the bike. The new owner is on here.. Just can't remember his username. I'd be guessing he'd still be running the same jets. It was 2010 EC300 with the 38mm ASII.

Been having some fuel leaking issues on my 2011 and as expected, poor mileage. Got a chance to pull it apart today, and was glad I did. The float level was quite a bit off from what I would consider "normal." I adjusted it so the float is roughly parallel with the edge of the bowl, not as easy to see as the older carbs. Unfortunately I can only estimate mileage as I dont have a odometer, but I expect improved mileage. :D

I did another hard 25 mi. yesterday. I tried to keep her on the pipe more and ride a gear taller whenever I could. Better mileage still: 25mi. on 3.265l. So, 117Km/tank or 72.2 mi.
I can live with that!
So, it seems that dialed in jetting and proper float height will solve the gas guzzling nature of the late model Gasser.

hard to beat those numbers. I'm temped to pull mine back out and adjust it closer to your height. In the summer time we ride a lot of high mountain trails and can make over 100 mile loops. In situations like that we carry extra gas in our packs, but having an efficient bike it key. I wonder how much your head mod plays into the fuel efficiency?

Unfortunately, I didn't get any exact nos. before I sent my head out. It was one of the first things I did. I've read on here that its good for 5-10% improvement.

Honestly, the gain in fuel efficiency from the head mod is a bonus. The real treat is that the power-band is smoother everywhere, idle is more consistent, and throttle response is better. I can pull a gear higher when I need.
Bottom line: It just makes the engine noticeably better everywhere. Thanks Ron!

Yeah its not that the you really see a reduction in fuel, you just use the fuel thats available more effectively after the head mod. You are achieving a cleaner burn that it more centralised around the spark plug. It makes things more consistant. In some aspects your bike will be making more power so where you would have had run at 3/4 throttle you might now be happy at 1/2 throttle. This also helps save on fuel. Clean jetting top to bottom is the number 1 fuel saver, and imo the head mod helps to achieve this much easier.

My experience with the head mod on a 300 was a mileage improvement of at least 10%. Before mod gas mileage: 22mpg after:25plus