Build a 200

Get a Beta 👍

I have wondered about alternatives, beyond re-using an ancient KTM motor.

Sleeving (and maybe de-stroking, I haven't actually looked and people here will know anyway so no point me googling it now lol) a 250 sounds interesting.

Drop that SX/MXC/XC engine into a 2011-2014 125/150SX chassis

Yes this is a viable option, im pretty sure it just requires some light modifications to the head stays. 

My wife has a 2018 150XC-W and its a sick bike and doesnt feel terribly different to the older 200s ive rode, one of those would be a good mx/woods bike, heavier flywheel and different gearing makes it feel way different to a 150SX.

Or a 200 crank and cylinder on a 2012 150.

Beta already builds an awesome 200. Same power characteristics of the older KTM 200’s in a modern chassis and KYB suspension on the race Edtion 

2015 ktm 150 with a 2004 ktm 200sx motor drops in no cutting or welding. Still to this day I liked that chassis.. the motor was badass… 200sx was only made in 03/04…there also was a specific 200sx pipe. It wasn’t shaped like the exc or mxc…

The great thing about the KTM 200 (and now the Beta 200) is that they are essentially bored and stroked 125’s including the 125 chassis.

Don’t do a sleeved down 250.

Looks like you'd need to sleeve a KTM 250 down 2.4mm, however you'd have to de-stroke it 12mm.

The bore change from a 125 to 200 is smaller than going from a 250 to a 200.

However the stroke change from a 125 to a 200 is more than going from a 250 to a 200.

Why not do a sleeved down 250? Crank/bottom end inertia and gearing? Initial port size (guess you could TIG and reshape, I've done it with a car cylinder head)?

Because you can build the 125/150 motor into a 200 using oem Ktm parts. There is also 175 and 188 possibilities with mixing 125 and 200 parts. Lots of build info on ktmtalk. 

I recently owned a Beta 200 Race Edition and way back my brother had a 200sx that I rode. Both bikes were amazing. The Beta was going to need a bit of love and modifications for it to be good on the moto track though. You might be able to get away with just a re-valve and maybe re-spring if you have the KYB fork and shock. I had the Sachs shock and didn't feel like it was going be enough. I ended up selling it and grabbing a full moto bike, but the Beta was the best bike I have ridden on trails and it impressed me with it's engine every time I rode it. Have a bit of regrets letting it go, but it just wasn't the right bike at the right time for me.

I bought an 05 200 for $1000, put about $500 into it to make it rideable and I was absolutely blown away the first time I rode it and how much of a weapon they are. I’m about 140 lbs and my only other bikes are KTM 125s and 150s, and the 200 motor is just incredible. Later on down the road I’ll either frame this 2005 and give it a nut and bolt build or find a 2015 or earlier roller to swap it into. 
 

I had always heard people rave about these 200s, but after riding one it blows my mind that KTM discontinued them. I’ll never sell this thing. 

I had a 2010 150 xc which is only a 144.  Did a big bore piston to it that brought it up to about 166. Also had a 17 150 xcw with a splitter in the reed side of the slide, higher compression insert and better reeds. The 17 pulled better than the older 166. Not quite like the older 200's but much less vibration and revved out better than the 200. I would go with the new Beta 200 with KYB suspension. Heard that the new Beta finally has a good turning radius.

All you need is 2002-2015 ktm 125/150 bottom end, ktm 200sx, 200 crank, 200sx Pv governer, cdi, and cylinder head. Dep, Doma and a few other euro companies still make pipes that are actually 200sx.. you have to get the 200 crank because the wrist pin is bigger.. the parts must be 03/04 200ax specific to make it correct. The mxc and exc have different mapping and long ratio transmissions..