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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!
Click for larger image of Emmett and the Team...
 Mini bike racing a NSR.
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.
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.
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.
Emmett's NSR50R...
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!
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.
Modified NSR50...
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.
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.
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!
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!)
NSR50R Mini Bike action...
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.
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!
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...
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.
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.
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!
Emmett campaigning his RS125R...
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
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
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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