posted on January 30, 2011 21:50
|The Malossi 80cc big bore kit has much larger transfer and exhaust ports. AF1 did a mild cleanup on our ports, equalizing their heights, chamfering them and removing flash. After porting we WPC treated the bore.
These small bikes are made to look like anything from a supermoto killer to a mini MotoGP machine and are marketed to those who think scooters are for sissies. The Aprilia RS50 and the Derbi GPR were the only ones that made it to the USA and the Derbi doesn’t really have parts support as Derbi went belly up in the American market. The RS50 is a somewhat rare machine and was sold in the USA for only a few years from 1999-2003. They are starting to be considered collector's bikes with nice examples now becoming expensive. At the time when we started this project, it was possible to find cheap ones.
|The Malossi piston dwarfs the stocker. We WPC treated the piston, pin and rings.
The RS50 is no joke; it has extensive aftermarket support in Europe where it is raced. Many engine kits and peripheral accessories are available for it. It has a Minarelli AM6 50cc water cooled engine with a six speed transmission. Way more sophisticated than your typical scooter or moped. The 50cc AM6 pumps out an amazing 8.4 hp stock which equates to about 7 wheel hp. The RS50 has a cast aluminum twin spar frame, a monoshock rear suspension and Marzocchi front forks just like a big bike. Large for its size, hydraulic Grimeca disc brakes grace alloy wheels. In short the RS50 shares more in common with big bikes than scooters and rides and handles much better than a scooter.
|You can see the size difference between the bore and the exhaust side ports easily here next to the stock cylinder. Note that the Malossi cylinder has 3 exhaust ports! A main one and two auxiliary ports at the sides.
Our example was purchased for $800 from a guy who only put 700 miles on it before crashing. After crashing he shoved it outside to rot since he was now afraid to ride. When we bought the bike it was in pretty sad shape. It was dirty and corroded. The crash had damaged the bodywork on the left side. The left side bars were bent and the shifter thrashed. However the bike was complete, it ran well and it was cheap!
Monday, January 31, 2011 4:57 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 10:15 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 11:57 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!
Monday, January 31, 2011 12:28 PM
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 1:04 PM
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 2:20 PM
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 7:31 PM
To be fair..the fuel economy of even a stock RS50 isn't that great....
Monday, January 31, 2011 7:45 PM
Our fuel economy will be much better. We know what we are doing sort of.
Monday, January 31, 2011 11:28 PM
Oh I'm sure you'll try. But generally the non Orbital two strokes, by their nature aren't terribly frugal.
Tuesday, February 01, 2011 9:24 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 9:34 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.
Wednesday, February 02, 2011 10:39 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 1:15 PM
"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 ;-)
Thursday, February 03, 2011 2:41 AM
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.
Thursday, February 03, 2011 8:55 AM
We read your minds, stay tuned to our future segments!
Monday, December 26, 2011 5:13 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 5:24 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.
Tuesday, April 10, 2012 5:29 PM
It currently gets 80 mpg.
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