So one day, I decided to get
a 4-stroke.
I was a 2-stoke guy for decades, at least for racing. Years ago I'd
owned a couple of overweight, underpowered 4-stroke dual sports,
but that was it. Not until fuel injection came along did I even consider
the possibility of owning a thumper. Then KTM decided to make some
really light 4-stroke race bikes. The 350XC-F received good reviews
for the kind of woods racing I prefer, so I picked up a leftover 2016
model.
New 2016 KTM 350XC-F
Of course the first thing I did was spend a bunch more money to set it
up to my liking, with lots of aftermarket stuff. My first focus was on the
steering damper. This is consistently my toughest challenge with any
new bike, as I prefer the Scotts damper mounted on top of the
handlebars. Apparently nobody does this anymore, as the options
were pretty much limited to the damper being mounted under the
handlebars. Which means the bars end up being raised higher. I
wasn't sure I'd like that, but it turned out just fine.

The other thing I wanted to preserve was the vibration-dampening
system  KTM uses for handlebar mounts. BRP was about the only
option with rubber mounts that would also allow for a steering
damper, so I spent the money and got a pretty nice system.
BRP sub-mount for Scotts damper
Tearing down the new bike
So let's explore my feelings and talk about
this bike's personality.
Switching to a 4-stroke put me on a serious learning curve. These
things are just...different. They sound weird. Mine was really loud, so
much that it hurt my ears when I cranked open the throttle. There
were more electronics, wires, things I've never seen before. In stock
form, the 350 XC-F stalled easily, partly because it was geared for
GNCC champions. After experimentation, I dropped a full tooth on the
countershaft sprocket. I also set the idle speed at a pretty healthy
RPM. After that, stalling was less of an issue, but it still happened.

On the good side, the 350 cruised awesomely through any kind of
conditions which involved sketchy terrain. In the rocks, the 350
hooked up better than any 2-stroke I've ever ridden. I can see why,
when I moved to St. Louis in the late-1990s, the Missouri off-road
guys embraced 4-strokes so quickly. The rocky terrain was made for
this kind of bike. The 350 is also a little smoother in the mud.

This smoothness was countered by less throttle response than a
2-stroke. Fuel injection helped, but the 350 wouldn't lift the front
wheel quite as quickly as the 250 and 300 two-strokes I've owned over
the years. The 350 also didn't turn as well as a two-stroke. I had read
about this, and it's true. However, it's not very noticeable in the
woods. I felt it on mostly grass tracks. Much of my practice riding is
grass tracks laid out on my pasture land, and there were times I had
to manhandle the bike around turns. The turning traits of the 4-stroke
are more than offset by how smooth the bike handled grass,
especially if wet. It was actually a bit difficult to make the rear wheel
break traction in dry grass, unless I was really leaning into a turn.

So I can see why 4-strokes took over the motocross world and are so
prevalent in GNCC and World Enduro Series racing. I can also
understand why 2-strokes rule in extreme enduros. Sometimes you
just need a quick blip of throttle to loft the front wheel in an instant.

As far as maintenance, the answer is yes...the 4-stroke engine
requires a little more TLC than a 2-stroke. Oil changes are more
frequent, the fancy oil required for these engines is expensive, and
you gotta buy a lot of oil filters. It's like most things...tradeoffs.

To work on the noise, I bought an FMF "Q" muffler...the "Q" meaning
"quiet". As usual, the manufacturer's claims were dubious. A sound
meter might say it's quieter than stock, but when you're trying not to
anger your neighbors, in actual operating conditions the bike is still
too loud. Likewise, the dyno may indicate more power, but I couldn't
tell a lick of difference. So basically I bought an expensive spark
arrestor.

One thing I did not buy was an aftermarket seat. Amazingly, KTM
actually sold me a bike with a seat that didn't feel like concrete. I did
buy the fancy Enduro Engineering complete headlight/taillight combo
with a wiring harness. That marked the first time in about a decade
that I had an actual working headlight and taillight on my race bike.

Final Conclusions
In 2019, I installed a Rekluse clutch, which cured all stalling problems
and helped me be lazier with the clutch. It was an expensive way to fix
an annoying feature of a racy dirt bike. KTM's XC line of bikes is
clearly designed for more open terrain that what I ride in the Midwest.
I was able to make my old 250 XC work because 2-strokes aren't as
stall-prone as 4-strokes. I could slow-ride through tight trees and not
hear the dreaded tick-tick-tick of a 4-stroke motor about to stall. And I
didn't have to spend $1,100 to fix the problem.

I also discovered the downside of the mass of electronics that make a
modern fuel injected engine run. When the engine wouldn't fire, I had
to get professional help. In 20+ years of subjecting 2-stroke engines
to unspeakable abuses, I was always able to make them run again.
Not so with the 4-stroke. At my stage in life, I was unwilling to take on
the added responsibility of being an electrical engineer, just to make
the engine run.

After less than 50 engine hours, I sold the 350 in April 2020...and
bought a 2-stroke.
November 2016
Final photo before the bike was listed for sale in November 2019.