because the four-stroke chassis was too tight down there.
The 380 has a large resonance chamber in the exhaust
manifold that made things difficult, but the rest of the
motor fit nicely. The air intake from the 250SX two-stroke
was essential, a plate was used to fill the gap left by the
fuel pump, and the Doma pipe was easily modified. The
ignition from a 250SX was also used. Within a month Bob
had sold his Honda AF500 and the Dungey two-stroke
THE TRIALS OF FRAME CHANGING
Just because a motor fits into a different frame doesn’t
mean it will work. Manufacturers spend a great deal of
time working out the smallest details about how a motor
sits in any given frame. That point was illustrated a few
years ago when aftermarket kits for the Yamaha YZ450F
became very popular. They moved the motor forward mere
millimeters, and it made all the difference in the world.
From year to year motorcycle makers change headstays
and motor mounts to fine-tune a bike’s handling. It all goes
into the soup. So, Bob continued with the project after it
arrived in California. No one was crazy about the KTM’s
suspension in 2013, so he found a used set of Showa
A-kit suspension. The fork was the factory version of the
single-spring SFF unit. From there Steve Piattoni at
Shock Therapy helped him make it all work. KTM’s
Factory Services wheels were used, and fresh
Dunlop MX32s were mounted up.
We got a chance to ride it after it was sorted
out. Actually, there probably wasn’t much
sorting done—at least we’re sure there was
no engine relocation involved. Jimmy and
Bob were just lucky. The bike turned
out to be one of the best-handling open two-strokes
ever. It seemed about 30 pounds lighter than the 500s of
long ago. It felt lighter than a modern 450 for that matter,
although there’s probably not much difference in the actual
weight. But, there’s certainly less rotational mass than
either a 450 four-stroke or a 500 two-stroke.
As far as power goes, the 380 was still plenty fast. It
can hang with any of today’s 450s in a muscle contest. As
you might expect, the workable part of the power bank
was narrower than that of a 450, but it was still wider and
smoother than we anticipated. It just didn’t like to be over-revved. You shift early, unless you really want to get to the
next turn quickly and are willing to hold on tight.
The nicest part was that we weren’t afraid of the throttle.
Yes, it made a lot of power, but not so much that it got
in the way. When you weren’t twisting it hard, you could
ride at very low rpm without any fear of stalling. That’s
something that modern four-strokes still haven’t worked
out. Some aspects of the bike, on the other hand, were
stark reminders that you’re dealing with 20-year-old
technology. It took a mighty kick and an iron foot to start.
Vibration was a little intense at higher revs, and traction
wasn’t always so easy to find. If you got a little carried
away with the throttle, it might keep on spinning until you
back off and start all over again.
Overall, though, we loved it. We just wish
there were more 380 motors laying around
in need of a modern frame. We’re not
saying that it was better, faster or more
competitive than a modern bike, but we
do believe that if open two-strokes were
this good back in the day, perhaps we
would still be riding them now. ❏
The “Dungey Dragon” has a 2000
KTM 380SX motor in a 2013 KTM