100 MPG Madness: Project Aprilia RS50

100 MPG Madness:  Project Aprilia RS50
By Mike Kojima

In these days of ever increasing fuel prices, MotoIQ's penchant for quirky small bore two wheel projects strikes again.  MotoIQ was conceived in a time when fuel prices were spiraling out of control and fuel prices actually touched $5 dollars per gallon.  We started a bunch of small two wheel projects at the time as it seemed like keeping our gas guzzling high powered rides parked only to be driven on special occasions might be a reality.  We wanted to show that fun could still be had at 100 MPG with the modification of alternative transportation.

100 MPG Madness: Project Aprilia RS50
Here we are somewhere midway through the assembly process.  We had some of the rusted steel bits re powdercoated by Embee Performance, these were the subframe, engine cradle, various brackets, swingarm and kickstand.  These parts were all a rusty black as the stock black oxide coating had rusted through.  We redid them in silver. Embee also redid the wheels and fork sliders.  The rusted fasteners were fixed by soaking in penetrating oil and wirebrushing to get the white corrosion off.  The alloy frame looked brand new with just a cleaning.

Fortunately the price of gas dropped rapidly and things came back to normal.  Lately though, fuel prices have begun a slower more insidious march upward, this time gradually over a longer period of time.  We think that this is because of ever greater demand of emerging transportation markets with a growing middle class such as Asia, India and Latin America.  With growing demand, we fear that high fuel prices may stay high and that $4 per gallon prices may be normal by summer 2011.

100 MPG Madness: Project Aprilia RS50
Putting together a bike, even a small one is harder than it looks.  It took us about a week to build the bike up.  Check out the carbon fiber gauge surround.  AF1 used to sell this part, but now you can only find it on EBay.

With the specter of high prices once again looming over our heads, we bring you yet another fuel sipping project; Project Aprilia RS50.  You might wonder what an RS50 is; it is really a very unusual machine.  It is a street legal, two stroke 50cc GP replica bike.  The RS50 was born in Europe as a source of cheap but sporty transportation for teenagers.  In most European countries, teenagers must ride 50cc restricted speed bikes until they can pass more stringent licensing tests and get older.  Bikes and Scooters under 50cc are much cheaper to insure as well. This is the reason why there are many pretty sophisticated small bore scooters on the market.  There are also a bunch of cool small bore motorcycles made by several manufacturers like Derbi and Cagiva.

100 MPG Madness: Project Aprilia RS50
Our RS50 starts to emerge reborn from a pile of rusted junk.


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Monday, January 31, 2011 1:57 AM
Hmmm, Mike Kojima king of LA barn finds. First a go kart, now a rare bike. I've only been lucky like that twice. Looks like a neat project, you going to show us the before and after of the poor thing?
Monday, January 31, 2011 7:15 AM
You mentioned the bike was crashed. Is damage to the frame or forks something you need to worry about? Or, did you measure to make sure a was not bent, or is it not a concern?

I look forward to see how this turns out!
Monday, January 31, 2011 8:57 AM
Any idea on how much holding capacity is lost by WPC treating the clutch? I've got a terribly grabby hydraulic clutch on my bike and would like to get a bit more modulation.

Love reading these all out small displacement builds you guys do. Keep 'em coming!
Mike Kojima
Mike Kojimalink
Monday, January 31, 2011 9:28 AM
I don't think WPC affects holding capacity. We know of really high powered cars using it on multi disc clutches.
Monday, January 31, 2011 10:04 AM
A quick search on my part yielded prices from $1300 to $2500 for these bikes. Every one of them mentioned a modification of some sort from bolt-on pipes to big bore upgrades so I'd say they're certainly fun to play with and tend to sell to enthusiasts.

My search was pretty wide ranging and didn't turn up more than a dozen bikes though :(

Mike: Any word on a new top speed with these modifications in place?
Monday, January 31, 2011 11:20 AM
Mike you're truly a geek.....lol
Look up Polini, Proma exhaust, Gianelli....all great companies with great products for those 50cc (well, none of them make 50cc displacement part....lol). They all go up to 80-85cc, some even higher (with water cooling radiators).
I remember growing up and always messing with Ciao and Si Piaggio's.....good times.
Another popular moped to modify was the Puck (from Germany). Very ugly moped, but porting and polishing the ports, bump up the comp, held quite a few hp. Some even reached 10-14 hp....lol
Anyway, have fun with the Aprilia.
Monday, January 31, 2011 4:31 PM
To be fair..the fuel economy of even a stock RS50 isn't that great....
Mike Kojima
Mike Kojimalink
Monday, January 31, 2011 4:45 PM
Our fuel economy will be much better. We know what we are doing sort of.
Monday, January 31, 2011 8:28 PM
Oh I'm sure you'll try. But generally the non Orbital two strokes, by their nature aren't terribly frugal.
Mike Kojima
Mike Kojimalink
Tuesday, February 01, 2011 6:24 AM
We are currently getting 80 mpg with 3x the stock power. Much higher compression ratio, better carburating and having squish in the chamber all help.
Wednesday, February 02, 2011 6:34 AM
Hi Mike, great to see someone giving the little two stroke back to it's former glory (and a bit more in this case).

I have to admit you are getting very good (excelent to be fair) MPG from this little 2T, as they were never know for being very frugal in terms of fuel consumption.
If you get it to make the promissed 100MPG (or roughly 2,35l/100km in my turf) I will get my hands on one myself. Hell, even diesel is too expensive these days :-)

If you happen to build a RS250 capable of maintaing at least the original performance and getting 50MPG, I'll ask you to send it overseas.

Mike Kojima
Mike Kojimalink
Wednesday, February 02, 2011 7:39 AM
We have an RS250 but are not sure what to do with it because its hard to register!

We haven't been able to crack 80 mpg yet. I think if we gear up more, its going to get too sluggish. We are geared much higher than stock, we will explain later.
Wednesday, February 02, 2011 10:15 AM
"The stock carb has water heating, probably for smog reasons."
Prob for icing concerns....

I am sure you looked into this but what tranny oil are you using? Also, chain and sprocket design/quality/condition will effect driveline loss a lot! Tires and pressures too ;-)
Wednesday, February 02, 2011 11:41 PM
Mike, sorry to hear that.
it's a shame those awesome 2T's are basically banned from public roads theses days.

You've got that right MXPOP, no o-ring chains, and some proper sprockets will fit in very nice too.
Mike Kojima
Mike Kojimalink
Thursday, February 03, 2011 5:55 AM
We read your minds, stay tuned to our future segments!
cameron campbell
cameron campbelllink
Monday, December 26, 2011 2:13 PM
where can you buy an rs50 in the states. i have an sr50 but i was looking to get the rs50 before i bought it
Tuesday, April 10, 2012 2:24 PM
hehe, good luck on the 100 mpg. I got around 50 mpg when it was more or less stock.
Any plans for the exhaust? Sadly there seems to be an inverse lineair connection because how loud the exhausts are and the power you get from it. I like sound of a high revving small 2 stroke, but at 100 something dB it gets old real quick for a daily driver. Especially because the damn police could hear mine wasn't stock from a mile away, i almost spend more money on fines than on the bike.
Mike Kojima
Mike Kojimalink
Tuesday, April 10, 2012 2:29 PM
It currently gets 80 mpg.
Sunday, February 23, 2014 4:36 PM
So, whatever happened to this?

An RS50 actually just popped up for sale from a friend of a friend, and I think I'm going to look at it tomorrow.
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