Interesting questions.

1. Why are 2 stokes maxing out at 300cc these days? ( I loved the old 350's, 380's 400's, etc)
2. Why are 4 stokes maxing out at 500cc? (I loved the old 550's and 650's)
3. Why does a complany like KTM make a slew of 2 stoke bikes with only 100cc difference between them? (200, 250, 300).
4. Does anyone sell the old super-light Husaberg models?
5. Is anyone going to sell the old Husky models (TE449/511 etc) in the US or elsewhere?
6. Does anyone produce the CTS (Coaxial Traction System) for any bike. ( I think it's fantastic ).
7. Is anyone producing semi-exotic dirt bikes available in the US that most of us haven't heard of?

News not always better grab a wr360 man up an learn to wring its neck!
Big bikes are hardly ever used to max potential so why have the extra cc and not use it?

A large bore 2 stroke wasn't just about max power. They had a character that the 300's don't. I've ridden the KTM300. It's fine down low and has a nice hook at the top but the middle is dead.
In all seriousness, I just don't know why all the manufacturers have stopped at 300. You'd think someone would break up the trend and sell a 360 or something.

I have watched and listened to a 300 KTM ridden by a pro rider on the pipe through the tight stuff in a hare scramble and it didn't flatten out on top. (I agree that the stock 300 KTM does flatten out) It is possible to get a 300 to keep on pulling with a few mods but Colo moto pretty much nailed it with his modern sissies comment.

Uh, the old Cagiva WMX300 (made by Husky until 2014) has lots and lots of upper mid and top end.

BIgger 2 strokes just end up beating the crap out of you and the power is hard to hook up. I rode a KTM 300EXC (1999) in Enduros for a few years... Later I bought a KLX300R and swore I was faster on that because 1). It turned a lot quicker in tight woods and 2. "didn't beat me up"... When the 300 got on the pipe you're going so fast, so quickly it could be real problems ;-).

Re: Exotic, what about Christini? I know it is just a 2 wheel drive mod, My buddy Wally Palmer rides Pro EnduroCross on them very successfully, and if you watch the Erzberg rodeo enduros, they work really well.

If you go back and check, more than 1 of the olden 500cc championships were won on ~360cc sized bikes and other sizes that were not true 500cc machines ... Not sure but I'm guessing just too much bike to get to the ground at that upper size ... Might be the same reason a 450cc bike did not get a single holeshot at last yrs MXdN ... 250s and 350s got the holeshots ...

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Now for why on the engine sizes lower than you want? Companies are only gonna sell a product that a profit can be turned on ... ~Everything else is out the back door.

While I haven't raced the TE449 I have now or the KTM 300exc, the 300 is no faster than any of the current 450 class enduros side by side.
The power valve tuning is adjustable to give the hit you are after, but at a test ride day by a local dealer over here in Aus, I went from the WR450 I owned, to the 300exc to the current model EFI WR all in the space of 1/2 an hour.
The KTM was actually slower in a staright-line drag than the 450s, but as you say, was harder to manage, it also had no engine braking & vibrated like it was broken.
In extreme enduro, it's lighter weight would be a god-send, but for average Joe, the bigger 4T bikes made the day easier.

Regards to 2 stokes here in down under in the bush our recent tests proved that a 250 2 stroke was faster through the bush than a 300 2 stroke in tight stuff and only 2% riders could ride a 300 2 stroke to its full potential and regards to 450 cc 500cc in the bush again 2% of people could ride this bike in bush at full potential , Yes in the sand on a straight line you could max these bikes out but it is very rare I would get into top gear , some of the blokes i know and have spoken to have won THE FINKE DESERT RACE, AD4A , some of these guys are riding 250cc bikes pegged sixth gear flat out and why 250cc more nimble and quicker in the bush . You want a bike alittle different try a OSSA 2stroke 280cc check this out an the babe.

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I had wondered what happened to the highland company. I had no idea that the owner died and the whole project was scrapped. Bummer

Where is the bike picture???

One of the most memorable rides I ever had only.... 30+ years ago was a Suzuki PE400 followed shortly after by a Kawasaki KDX420. GREAT slow speed, nice midrange, super hook on top. Honestly, todays 300s are just pumped up 250's. They don't have that big-bore, broad powerband that the 400's had. A big bore 2 stoke can be tuned to be whatever you want it to be. But an under-tuned (?) endure tuned 400 is a great motor displacement.

PS: bring back the Husaberg 650!

Shame this still hasn't made production with the DI.....

Alright, so l think the ideal bike would be a Service Honda CR500, re sleeved to 400cc, drop compression slightly, add a lighting coil, perhaps a flywheel weight and a Recluse Clutch... OH YA!
Actually, who needs a flywheel weight if you've got a Recluse?

It's called a ZipTy WR511.