fastest 50cc

[earlwb]

In 2006 a 50cc bike did 121.439mph at Bonneville. 137mph one way.
They sort of used an Aprilla engine. I doubt there was much left that was Aprilla in it though.
But before you get too excited, the record to beat was set in the netherlands in 1981 at 137.961 mph using a 50cc streamliner 50cc motorcycle.

Now with scooters some guys are reporting going 65mph or faster. One fellow with a Nitrous system got over 80mph.
65mph looks realistic as one of those water cooled Kymco's with minimal mods can do that.

Aprilla has this on their site about setting a speed record of 84.36mph on a 50cc road race bike.
www.apriliausa.com/njb_dettaglio.asp?id=303
After they worked out the bugs of course, years ago, the Japanese dominated the 50cc GP races with their multi-cylinder 50cc GP race bikes.

I think that my best memories were racing 50cc road racing bikes many years ago, at least until I got too big and fat for it. I grew up. Like these here:
www.madmalc.screaming.net/50cc%20Motorcycle%20Racing.htm

Check out the cute engine in the back of the streamliner here:
www.geocities.com/buddfab/buddfab3

METRAKIT SETS TWO NEW AMA NATIONAL RECORDS FOR A 50CC MOTORCYCLE

John Buddenbaum and Eric Noyes of Sunnyvale California with the support of Metrakit USA and Cycle Imports INC. set two AMA National Records with a 50cc motorcycle streamliner. The motorcycle was designed and specially constructed by them in John’s fabrication shop in Palo Alto California. Powered by an Aprilia 50cc (Minarelli AM6 engine) modified with METRAKIT pro race engine parts.

On Monday September 4th at the International Motorcycle Speed Trials by BUB held on the Bonneville Salt Flats in Utah, Eric Noyes drove the streamliner to a new AMA National Record for 50cc streamliners on gasoline (S-AG) with a flying start one mile two way average of 121.439 mph.

On Thursday September 7th John Buddenbaum drove the same machine, modified to run on fuel, to a new AMA National Record for 50cc streamliners (S-AF) with a flying start one mile two way average of 133.895 mph.

The highest AMA record for a 50cc motorcycle was set by H. Muller at Bonneville in 1956 in the Blown Fuel class at 121.700 mph (S-AB) using a machine built by the NSU factory. This class no longer exists, current safety regulations mandate equipment that makes today’s streamliners bigger heavier and safer than the old classes.

The highest recorded international speed record (FIM) for a 50cc motorcycle: flying start one mile average speed was set in 1981 in Lelystad, Netherlands by Jan Huberts at 137.961 mph (222.026 km/h) with a streamliner powered by a
Kreidler engine.

John and Eric will be participating/competing in the 2006 Bonneville World Finals October 11th -14th. If they can add just over 4 mph to their last record performance they will then hold the distinction of having built the fastest 50cc motorcycle ever officially timed.

For more information on the Buddfab Streamliner go to: www.geocities.com/buddfab/buddfab3

For more on Metrakit parts visit: www.metrakitusa.com

[motomech]

In 1990, I bought a new Honda NS 50 with the intent of going racing. I had been eying mini racing, but I didn't want to go with a YSR, mostly because I didn't fit(6'0" and a svelte 170# at the time), but also I didn't think much of it's antiquated power plant.
The project was inspired by an article I saw in a Japanese Mini-Moto magazine that some thoughtful person in Japan had tossed in a box of Kitaco big-bore kits I had ordered.
The text was in Japanese of course, but the photos showed an stereotypical Japanese technician in a white lab coat standing next to two disassembled engines layed out on a bench. But the two engines were named in English, NS 50 and CR 80.
I was intrigued, and took the article to the local university's language department for translation. When I went back, the person who did it wasn't there, just a note that said, "no fire". Hummm...
Well, I knew one thing though, the CR 80 was air-cooled and that nailed down the years down to a couple of mid '80's models.
With the two engines layed out on my bench(minus the lab coat), it became apparent that there was a lot of interchangeability.
The 80's close ratio tranny and internal rotor ign(including CDI) bolted right on/in the NS(stand for Not Slow).
The ported cylinder was bored to fit a KX 60 piston, which with the stock NS crank came to 57cc's. The class limit for modded 50's was 61cc, to accommodate the stroker YSR's. The cylinder head's combustion chamber was reshaped on a lathe, adhering to the 1/3 squish band rule. The squish was real tight, .010" to .015", if I recall right.
All this came together real quick, but the carb and pipe took some development time. The first try was the CR 80 bits, because I had them. The 28 m/m round slide fitted ok, but cutting and rewelding the CR's up-pipe was a challenge. Lot's of carbon and I didn't have a wire-feed. Anyhow I got them on and while the Frankenpipe was not pretty, it worked well. Too well. The bike was a rocket from the git-go, until I seized it(ever notice that two stokes run best right up to the point they seize?). Attempts to jet it safe proved fruitless and I came to understand that the pipe wasn't going to work, It was too fat, creating a negative wave pulse that the carb couldn't deal with.
Next try at a pipe. I ordered some cones from Air Cone and tried to make my own from scratch. Easier said than done as I discovered the problem that plagued all pre cad-cam pipe designers. To make the center cone the diameter I wanted, the cone angles became too steep and became counter-productive. At least the metal was clean and I could get some decent welds.
With a serviceable pipe, it now became clear that the carb was too big and a 26 m/m round slide Mikuni was fitted.
Chassis modifications at his point were zero but I attended my first race anyway. It was at the old Las Vegas Speedway and was a silly venue for 50's. WOT with one downshift for the entire lap. The Honda easily ran away from the YSR's and I thought, "piece of cake". Boy, did I have a lot to learn!
The next race was at the Adams track, A fast, banked cart track near Bakersfield. I got waxed, but at least I wasn't last. The stock tire and frt. drum brake didn't inspire confidence and I had not a clue what I was doing(I remember scraping the shinny knee pucks behind my truck so they didn't look so new). The Pros(who were not at Vegas) were crossing my bow like Nelson's warships "crossing the T". Obviously, both the bike and myself needed a lot more work. I did meet a guy who built me a pipe, a beautiful hydro-formed number that really woke the motor up.
Brackets were machined to adapt a YZ 80 caliper up front and the rotor was from an old CB200 mechanical disc brake model. The tire problem was solved when I was able to beg a used set of tires from the Pro RS125 riders(hey, they were worn out on one side. I flipped them around, only a 50). Tiny Michelin slicks from the front, they were so small, that from a distance, they looked like inter-tubes.
With the addition of clip-ons, this was the basic bike that I raced for four seasons.
I got better(why can't they all be left turns?) and if I could keep the leaders in sight, I had a chance. While the air-cooled YSR's lost power in final laps, the liquid-cooled Honda ran as strong as ever.
A Kiehin 28 m/m flat slide(PWK) was installed and when I finally got it dialed in, it was like adding a supercharger! It was in this configuration that I was clocked at 74 m.p.h.(By radar) on the slight uphill starting straight at the Streets of Willow track(It was never dyno'ed, I think 15 h.p. at 15.000 r.p.m. would have been close. With a lighter rider and the right gearing, 80 m.p.h. would have been possible). At this particular track, I was able to pull the field by six lenghts at the start, only to have them breathing down my neck by turn three. I studied Kieth Codes "A Twist Of The Wrist" till my head hurt(why couldn't he just come out and say what he meant? Well I guess he couldn't sell two more volumes if he did). I came to understand the lines(dirt racing didn't prepare me for this) and I managed to wobble to a fifth place Expert for the year.
The Big Wheel did have the advantage of the higher handle bars because nobody wanted to get their knuckles raked over in a turn. But the skinny tires didn't offer the grip of the YSR's 12" fatty slicks and I couldn't get the speed though the tight cart track corners.
So I started over and built a "small wheel". To keep the front end geometry reasonable with the 12" wheels, I turned the leading axel forks around so they became trailing axel forks. I meant losing the stock fuel tank and I mounted a very rare alum tank from a mid '70's Yamaha MX175. With the aftermarket spun alum. ysr wheels, it didn't weigh anything. I could pick it up and walk around with it!
The "World Mini Championship( ::)I know, they would murder us in Europe) was at Reno that year and that was where it's first and last outing took place. The Reno cart track was new and reflected the trend to "square-up" the curbs to keep the cart guys from putting their inside wheels on them and loading up the chassis. It was one of these curbs I clipped and put me into a memorable earth/sky earth/sky experience. I remember calmly watching the late afternoon sun reflect off the spinning frt. wheel as the bike catapulted over my head(The rider behind me rode under it, hitting and ruining his helmet in the process).
[Crashes are funny things, some unfold like in slow motion, other blind side you. maybe we should do a thread on crashing?].
Crashing always hurts, but the pain of that one lingered. I had won the first heat and was leading the second. But almost as bad, I caved in the side of my beloved MX 175 fuel tank.
Back in the shop, I tried to blow out the dent with compress air. I guess I over did it, because it blew up like a balloon

P.S. The little Honda engine was a rock. I only changed the rings once a season(13 or 14 races) and crank brg.s every other. Neverm the crank, amazing. It could have been taken to an even higher state of tune and remained reliable.

P.S.S. I.M.O., Aprilla's claim of 25 rear wheel H.P. for a production 50 seems unreasonable. Do the high performance 80's even make that?

P.P.S.S. Sorry, no pictures, all my personal belongings were stolden in customs when I moved here to Costa Rica.
A stock NS 50 looks like this;
gallery.mvagusta.net/twoeleven/photo/21012/mygarage/

[egarzon]

i finally fixed my speedometer and was surprised to get 45mph on my Roketa Bahama Mama 50 and it wasn't at full throttle!!!