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Mini
Bike racing is extremely popular in the States.
Emmett Dibble's feature explains the virtues
of campaigning Honda's NSR50 and NSR50R, and
provides a few tuning tips into the bargain! |
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Mini
bike racing a NSR. |
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The
2004 year model line up features something new
at your local Honda dealer here in the United
States. As far as I know, it's the first time
HRC (Honda Race Corporation) has sold a model
directly off a traditional dealers showroom
floor. Previously in the US you had to either
purchase your new HRC model machine either through
the "official" HRC dealer or have
a grey market dealer import you one (or do it
yourself) from Japan. |
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The
'04 NSR50R is available at from any dealer who
ordered them. The basic NSR50 has been out since
the late '80s and was raced by mini bike racers
almost immediately. Here in the US however,
it was never officially imported, so the race
mini bike of choice has always been the Yamaha
YSR50. While a perfectly acceptable mini bike
racing platform, to be competitive the YSR needs
some very heavy work. The pre-HRC NSR's were
the same to an extent, but in Japan have almost
always been the weapon of choice for obvious
reasons. For the sake of this article I'm going
to discuss the advantages of the older NSR's,
race modifications, and why the HRC NSR is the
hugest bang-for-buck in mini bike racing right
now. I'll cover the suspension/frame, wheels/brakes
and motors. |
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The
suspension on an NSR50 is quite good compared
to the YSR. They both come with a spring on
a stick for rear shocks, but both benefit when
quality units are installed. I am pretty sure
no one makes a YSR shock anymore, but there
are several quality manufactures for the NSR.
The Forks are 30mm and have springs and dampening
rods in both legs. This may seem a mute point
unless you know that a YSR comes with only one
spring, and dampening in only the left fork
leg. On a stock NSR the biggest improvement
to be made on the front end is to install an
actual upper triple clamp. Like the YSR it uses
a stamped sheet metal clamp that uses the clip
on bolted down to hold it in place. The 30mm
forks are huge compared to the YSR's 28mm, and
with the clamp there is really no need for a
fork brace. 10 - 15wt oil at the stock level
is a very good place to start. The rear swing-arm
has rubber bushings like the YSR, instead of
conventional bearings. You will have to have
someone fabricate bronze or maybe Delron bushings
to strengthen up the pivot. As with a YSR, the
PITA is removing the rubber bushings. |
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The
NSR50R
is all about being from HRC in the suspension
department. The forks are 30mm longer for more
travel, have better damping rod settings, and
has a aluminum upper triple. It also has 2 different
fork spring rates you can order, and preload
adjusters as standard. The clip ons actually
clamp to the fork leg and are less then $40
each from HRC. The rear has a standard issue
mac daddy Showa racing shock with remote reservoir,
preload, compression and rebound adjustments.
While most of the aftermarket shocks are in
the $3-500 range the HRC showa is $800. Is it
worth it though? I dunno?! The swing-arm comes
with sweet needle bearings and the steering
head is lengthened 30mm to accommodate the longer
forks. The NSR wheels are aluminum; 2.5 front
, 2.75 rear, both with disk. Like any race bike,
you change the front line to stainless and use
the appropriate DOT 4 fluid. The YSR uses aluminum
hubs with steel wheels which are heavy or you
have to buy aluminum replacements. The YSR front
disk is only about 2/3rd the size of the NSR's
too, and it uses a rear drum. To be fair most
riders don't use the rear brake on mini's so
it's not as big a deal function wise but the
rear disk of the NSR is much cooler. The YSR
wheels are only 2.5" front and rear which
puckers the rear 120 series tires a bit to much
unless you pay for the aftermarket wheels. The
NSR wheels fit the 110 front and 120 rear race
tires currently being made perfectly! |
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Wheels
and brakes on the NSR50R are standard late model
NSR50 street type, which is fine. They even
come from HRC with Dunlop TT91's which are the
race tire of choice for most mini racers. They
are basically the same "B compound"
used for the GP125 slicks and have fantastic
adhesion. Wear is good also. Depending on the
tracks and rider skill level, a set can last
up to a years worth of racing. The HRC front
pads are sintered and should last at least a
year. Depending on how you like your lever to
feel, the only real upgrade for the NSR50R is
the front brake line. It's rubber, just like
the street version of the bike. Some people
will also prefer IRC or Bridgestone to the tires
that come on the HRC bike. |
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Motors
are where you can go from mild to wild, and
it all depends on what you want to do. The basic
motor architecture on the NSR has been around
for quite a while which says a lot for a design
that is still competent and hasn't been changed
for almost 15 years. Depending on the model
year, it will be either an AC-08 or an AC-10
motor. Both are "basically" identical
mechanically. The differences are ignition,
cylinder, and clutches. |
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The
early 08 came with a GT-2 cylinder; the later
08 and then 10's came with the GT-4 cylinder.
They are basically the same but with minor port
height changes. Being that it is a mass production
scooter motor, the actual port windows are a
bit rough and not shaped as well as they could
be. If you are wanting cheap bang-for-buck,
having a high quality tuner clean up the cylinder
and square up the ports really wakes up the
motor. The stock timing of the ports is really
good so don't spend money or time trying to
change them. You can go backwards real fast
in the tuning department. The heads on both
motors are the same and the volume is HUGE.
The compression ratio listed by Honda is 7:1.
You can run 87 octane fuel all day long and
never have a detonation problem. Likewise the
squish is well over 1mm. A very cheap hop up
is to just have the head milled down to the
squish area. Your squish will still be well
over .5mm still be very safe. This will bring
the compression ratio up to around 9:1 which
is still low enough so you can use 91 octane
pump gas with no problems. Some slight port
changes and lower transfer additions, plus getting
the volume down even lower and machining the
top of the cylinder to get the ratio up around
12:1, will really make it grunt, but all of
these modifications should be left to a very
experienced tuner. |
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The
bottom ends are identical except for the main
shaft and clutch. The 08 uses a 3 plate clutch,
the 10 a 4 plate. Unless you tend to fan the
clutch or have a highly modified motor there
is really nothing wrong with the 08 if that's
what you have. You will need to remove the clutch
cover and clutch to remove the oil pump and
kick starter. The blanking plugs are readily
available from Honda using the HRC NSR50R part
#'s, or match them up at a local auto parts
store. You'll also want to remove the gear position
switch and plug the hole, but it isn't completely
necessary. You can just cut the harness and
leave the switch. Some people do this simply
because they don't have access to a tamper resistant
torx bit that they are installed with. A trip
with the bottom end to the local bike shop and
$5 in a mechanics pocket will get them out for
you. Also, when removing the oil pump, don't
forget to put 2 shorter screws back into the
mounting holes. They go straight into the transmission
and will puke oil everywhere if not sealed! |
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The
ignitions are a source for head aches if for
no other reason than the plethora of choices.
The 08 motor uses a traditional charge and trigger
coil - simple. The only real mod is removing
the lighting coil. That will keep the charge
coil cooler and saves a chunk of weight. The
10 uses a alternator. The voltage is regulated
& rectified then
the CDI can use it. This system is used so the
street version has a bright headlight and doesn't
flicker at idle. We are racing and couldn't
give a rats butt about that! It also ads to
the complexity with the extra reg/rec and needing
a battery or capacitor (battery substitute).
The other 2 drawbacks are that it's heavier
(doesn't really matter in the big scheme of
things) and is not adjustable (matters a much
more in the scheme of things). Either ignition
will need a different CDI module sense the Japanese
laws speed regulate 50cc scooters to 45mph.
Here again there are a multitude of choices
from cheap to expensive, and they all claim
to be best! To be fair I have tried cheap and
expensive, and there's no HP difference to be
found. (I'll receive hate mail over that statement!) |
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Getting
the fuel into the bike is relatively easy. Especially
if you are racing kart tracks. The stock cage
cleaned up with Carbon Tech reeds is the bomb.
The HRC glass reeds aren't bad but the Carbon
tech reeds are much more crisp. The stock carb
is very adequate. It is a 18mm Kehien. The largest
I'd go is a 20mm Minkuni VM. It requires you
to modify a YSR Mikuni flange mount manifold
to fit it but it's very easy. Just use a good
drill press and the NSR intake gasket as a template.
Some people like using a Mikuni TM24mm carb
but I can assure you the HP increase is negligible
on a 50-60cc motor configuration and the drivability/jetting
is VERY hard to get right. Basically it's just
to big. Also use a quality foam or cotton screen
mesh filter. The HP difference isn't worth it
the first time you suck a bunch of dirt or a
rock from crashing. Obviously if you are converting
a street bike you will have already pulled off
all the street stuff. Air cleaner, oil tank,
horn, battery etc. |
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The
only real thing left is the pipe. The stock
pipe isn't "bad" but it does
leave a lot to be desired. Aftermarket pipes
are pretty limited here in the States. I don't
know why, but Japanese aftermarket pipes are
incredibly expensive. They are VERY proud of
their pipe making ability, and while I do use
one, it is only because I got a screaming deal
on it! Much cheaper alternatives here in the
States are to either order a Metra Kit pipe
or Tommy Crawford pipe. I have no experience
with the MK pipe but I do have experience with
Crawford, and his pipes rock! |
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Notice
I never said anything about fuel, oil, or jetting?
That's because there's such a range of possibilities
and variables I am not even going to try. You'll
need to figure it out or have a tuner/someone
you trust figure it out. The stock carb will
run in the 102 - 110 main range and the 20mm
VM will run in the 110 - 140 range depending
on fuel, oil ratio, oil, weather, planet alignment
etc... |
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As
far as wild hop up goodies just look in a Kitaco
or Takagawa catalogue. Close ratio transmissions,
dry clutches, inverted forks, internal rotor
ignition kits... all with equally wallet draining
prices and dubious lap time improvement. The
ultimate and possibly most cost effective engine
kit is from JHA. They have a carb, pipe, reed
cage, and cylinder head kit that is only around
US$1400. For JHA stuff that is a bargain! The
only problem is it is 70cc's so it pretty much
eliminates you from all but maybe one or two
classes, plus with the huge increase in power,
things are going to wear out/break much quicker. |
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One
of the strong points of the NSR is it is much
like the YSR as far as maintenance goes. If
you remain fairly stock and do good motor builds,
use good oil and keep your jetting under control,
they are just about indestructible. The bottom
end will go at least one and possably 2 seasons
on a crank. The top end will go a season on
a piston and rings - half a season on a set
of rings if you want a little more power. The
prices on parts are very reasonable too. |
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At
around $3000 for a brand new NSR50R at the local
Honda shop, they are about the biggest bang
for the racing buck there is. They come with
an HRC manual just like a 125, 250 or even the
NSR500V. You literally ad premix, set tire pressure,
set suspension sag and go ride. Easy! |
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All
of the information contained in this article
is worth exactly what you have paid for it.
In other words your milage may very, there is
more then one way to skin a cat, etc, etc, etc.
I have been racing for 14 years now. I have
raced/tuned a NSR50 and a NS50R for over 2 years
now. I have raced YSR's for 10 years. RS and
TZ 125's and 250's. Complaints, arguments, critasizm
please keep to your self. If you need more information
you can contact me at
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Emmett
Dibble
Rosharon, Texas, USA
CMRA #6, '04 F6 Endurance Championship, NS50R
TMGP #41, '04 LWSB 3rd place Endurance Championship,
NSR50
TMGP 2004 12 hour Endurance 3rd place HWSB |
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The
information expressed in this independent artical
are the views of the author only, |
and
therefore may not reflect the views of . |
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