The 50cc road racer – from 25km/h to 65km/h for 60€

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Dit onderwerp bevat 9 reacties, heeft 6 stemmen, en is het laatst gewijzigd door Wilk1985 5 maanden, 1 week geleden.

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    Topic starter
    Berichten: 21

    Hello again guys. First I want to thank everyone who were so helpful and nice when I wrote my first thread here, you gave me a lot of knowledge, inspiration and courage! This project would probably not have been the same without your help!

    Secondly I would put out that this project is possible to copy for 60€, but that requires that you already have lot of different tools and machines, a space to be working in, a lot of time and dedication. I am no engineer, and I have learned a lot in this process, but I think it is fair to say that this is still on a pretty moderate to advanced level, and will require some effort. This is not a quick fix, this is about embracing the effort and be willing to get your hands a bit dirty.

    This project is an example, and this text is about how I did it, there are many other ways out there. I will not write about everything, since there are so many good guides/threads on this forum already, but I will try to make any interested reader is able to follow along as good as possible.

    One last thing, I had a lot of fun reading Graham Bells book about two strokes tuning, I really felt that it was a good start for me. I also recommend that you read more threads on this forum, and also scan youtube for knowledge too. There are two very nice youtube videos made by a Danish enthusiast that I can recomend, simple search for “piaggio moped engine rebuild” and ” piaggio moped engine tuning.” A good knowledge base and a good understanding of two stroke engines made me feel less flustered with things, or at least it made me feel more certain about what I was actually doing. I am still a novice in the magical field of the humble two stroke engine, but here is my first attempt:

    I started out with a Ciao from the ‘ 90s, in fairly good condition, with an untouched engine. It did run at 25km/h, which is how it came from the store all those years ago.

    It had a 7/10 dell’orto carburettor with a standard air filter, a 7mm inlet and a fully restricted inlet window. It also had a 105 mm pulley and an original exhaust. But it was untouched and in very good condition. The previous owner was an old man who had been taking very good care of his moped since he bought it in the 90s.

    Here is an shopping list, the bare minimum to make this work:

    66 nozzle 2€
    80mm pulley – 3€
    937 mm belt – 8€
    Giannelli City Power exhaust – 37€
    Spark plug NGK B7HS – 3€
    Aluminium plate with a 3mm thickness – 5€

    Here is also a list of optional items:

    Polini clutch springs (stainless without paint) This would give you a little more time before the clutch shoes grabs the clutch bell meaning a little higher RPM before the engine starts to driving you forward. This is good for someone who is doing smaller pulleys than standard – 9€

    A 13 or 14 mm dell’orto SHA Carburettor, for someone who simply feels like it is worth paying for a premade carburettor instead of bore the standard one. – 36€

    A racing air filter or any type, for someone who simply feels like it is worth paying for a premade racing air filter instead of modifying the standard one. – 7€ to 15€ depending on brand.

    Now let’s cut the chase.

    This part have already been written a million times on this forum, and therefore I will not go through it in detail at all. I will put some extra focus on the later part of this tuning process.

    I first removed the engine and took it apart. I gift all the parts a good clean and made sure all the bearings were healthy. After that I removed the hardened steel restriction in the inlet with an especially home-made tool, a hammer, a file and a heat pistol. It was not fun and I almost gift up. But it came out and I managed to keep the inlet intact. After that I filed the inlet from 10mm to 13mm with a rotary tool driven by compressed air. A standard rotary tool could also have been used, or even a dremel. Though I do not think dremel still sell rotary burrs with bigger diameter than their 3.2 mm standard. I used an 8mm carbide burr for the actual enlargement of the inlet.

    After that I used a regular round file to make the inlet window larger by hand filing it. There is plenty of guides on how to do this and also on how to enlarge the inlet.

    Now I could have gone to the next step and bore the standard carburettor and modify the stock air filter, but sometimes time is short when you work full time, so I decided to buy a used dell’orto SHA 13 mm with a Malossi racing air filter for a small sum of money. I gift it a good clean and made sure I had a nozzle in the right range.

    After that I installed the 80mm pulley and the matching belt. I went for malossi on both, but I know for sure that the cheaper options are just as good.

    Then I changed the clutch springs to new ones (polini) and also the clutch shoes (to newfren) since the old ones were worn out.

    The clutch with the new clutch springs and clutch shoes installed

    After this I did put everything together, including the new cooler spark plug and the Giannelli City Power exhaust.

    It was truly a new moped at this stage, compared to the ultra-restricted version prior to this. It had good acceleration and an honest GPS-measured top speed or 52-54 km/h depending on the wind and the level of the road. Where I live we have no super flat roads. So I think it is fair to say it ran in 53km/h. At this stage I never tried with the 70mm pulley I had bought out of curiosity. It will be tried later, though.

    Now to the fun part. In the standard cylinder set up, we can see in this picture that the piston is covering a total of 3mm of the inlet ports and the exhaust ports when the piston is at BDC.

    If you look closely you can see how the piston is covering the bottom part of the ports.

    This is off course no good. So I decided to raise the cylinder with a homemade 3 mm aluminium gasket.

    But we cannot just raise the cylinder without compensating for that. Therefore I took the cylinder to a mechanic workshop and asked them to remove 3 mm from the top of the cylinder. This could be done at home, if you have a lathe or a milling cutter in your garage. The guys in the workshop used a lathe and the results you can see on this picture. They asked for 50€ to do this job which is fair around where I live.

    I chose to leave the cylinder head intact, due to the fact that I feel like it might not be worth to mess around with this time. I might change my mind in the future. More about that later.

    After that I made three boost ports in the cylinder using the idea I got from another forum member. Thanks a lot for this genius idea! I made the ports those using a pillar drill, a round file, some sand paper. I also made two windows for the transfers. Before you point it out, the boost ports are not symetrical to the transfer ports. And the reason for that is me, because when I made the first port I realised I would not be able to make a second port where I first hade planned to, at least not with the tools I had available, because then I would have risked to go to close to the hole for the stud. If I had realsed that earlier I would instead have gone for 4 boost ports, two on each side of said stud. So now I ended up with 3 ports, but the placing of them is not symetrical. Does it matter? Perhaps Graham Bell knows. Anyhow. The results can be seen in these pictures:

    Now, as you can see in this picture, the bottom of the ports are perfectly aligned with the top of the piston:

    I also gave the exhaust port some good cleaning with a fine sandpaper, but other then that I left the exhaust port intact.

    Everything finally put thogether with some grease on the new home made gasket:

    I changed the ignition points from 4mm to 3.5 mm just in case and after that I put the enginge back into the ciao.


    It started straight away like it would normally do. I took it for a warmup run at slow pace around the neighborhood. Then I went back home and grabbed the GPS. As I mentioned before, I have no ultra flat road close by, but after some driving back and forth I concluded that it runs in 61km/h. Whoa wait a minute, didn’t the title say “from 25km/h to 65km/h”? Yes it did, and the reason for that is the 70mm pulley that I tried later the same day. With the 70mm pulley I did reach 65km/h, on a fairly flat road with abolutely no wind. After some driving aroud I settled for the 80mm pulley, not because it did run bad with the 70mm pulley, not at all, It is just that I live in a place with a lot of hills. If I were to ride it for longer distances, I would definetly put back the 70mm. So for me, the 80mm pulley turned out to be The perfect Pulley.

    Here comes a list of things left to do if I had truly had been chasing the absolute top speed and were ready to give a little on long term engine reliability to reach it.

    • Mill a little bit more than 3mm of the cylinder and deepen the combustion chamber on the cylinder top accordingly. This would increase the compression and therefore the mid registry a little bit.
    • Modify the crankshaft to increase the inlet timings up to perhaps 175-180°. This would generate higher rpm and therefore higher top speed, though it will also increase wear and shorten the life span of certain parts of the engine. After all, we are talking racing here.
    • fIncrease the bore or the cylinder from 38,2 mm to 41mm, 42mm or perhaps just 43mm for the one who is not faint hearted. This would of course require a new piston. This would push the borders of the integrity of the cylinder a lot, but then again, it is possible. This would probably result and a little extra horsepower.
    • The inlet could be filed to 14 mm instead of the traditional 13mm. The carburettor could be bored accordingly to match those 14mm. This would provide some extra mixture and could probably crank up the engine a tiny notch.
    • The exhaust port could be enlarged it by sanding 0,5-1mm in the top of the port and perhaps a little bit on the sides or the top or the port. There is good pictures and decriptions on how to do this in the Graham Bell book.
    • One could also pick a more racing oriented exhaust pipe made for higher top rpm instead of the more discreet one that I picked. I have heard good things about the Simonini Calibrata, but there is many good pipes out there to choose from. Just make sure to match this with a correct nozzle and perhaps some more air through the air filter.
    • One could probably also modify the piston a little bit by cutting small windows or the bottom skirt towards the main ports and make small grooves in the top matching the ports to feed the engine a bit more mixture. The later could interfere with the compression and the squish values though.
    • One could also buy a used complete variomatic system and install, even though it is not stock on the Piaggio Ciao, but I thought I should mention it anyway.
    • The boost ports could probably be even more aggressively made, and also be ported into the crankcase for that extra little boost.
    • And last but not least, for someone who really want to delve deep into the mystery of two stroke tuning, the two main ports on the cylinder could also be enlarged. This could be done, and it could reap good end results, and it could also ruin the cylinder. But for anyone who wants to try and push the stock cylinder to the maximum. Give it a go! Just remember to port the carter accordingly.

    Maybe I will try all this someday, for fun, just to build a racing engine using the stock cylinder and a stock carter. Until then. I am so happy with my version, a bit more tuned for long distance driving and a longer life span, but still with bags of fun to ride around on.

    If one were to do a complete overhaul of the engine like the suggestions in the list above, it would probably be good the decrease the distance between the ignition points all the way down to 3mm, to increase the life span of the enginge.

    I hope this reading might be interesting to someone. Please feel free to comment, give feedback or ask questions.

    Once again, big shout outs to all you guys who helped me out!



    Topic starter
    Berichten: 21

    Guys, I absolutely don’t know why, but when I pressed Verzenden to publish this, something changed the word “gave” to “gift” and the word “of” to “or” in my text.


    Topic starter
    Berichten: 21

    Also, the GPS measurements I used before was way off. It was an app in my phone. This time I have used a GPS for cars, so my speed measurents in this article are now correct. When I wrote before in my previous posts that I drove 54 km/h on a 105mm pulley I was wrong. It was actually 43 km/h with a real GPS. Sorry for that!


    Berichten: 6456

    Wow, you made it a good and fun article to read. There’s only one tiny miny bit that annoys me. In the pictures your piston is not as clean as the rest of the engine. Why not get rid of all the carbon on the top of your piston when your engine is opened up already. 😉

    Anyway i’ll hope this is not your last and final work here on the forum? I would like to read more of your input.


    Topic starter
    Berichten: 21

    Thanks for your kind words Martino! I had a lot of fun writing it. Haha, I was about to clean it, but then my dad walked by and said “young lad, you know that if you clean up the piston you might lose some compression”. So I laughed a bit to myself and left the carbon on top just to make him feel like he knew what he was talking about  😀

    I will clean it one day tho, dont worry!

    One more thing I might forgot to say is that after the modifications of the cylinder were done, it was not only the top speed that went up, but also the power in the upper rpm registry. All of a sudden it showed good acceleration even when I was close to full speed. And from that it made it super fun to ride on the tiny and curvy asphalt roads in the forests around where I live!

    Happy days:


    Berichten: 2177

    Wow, you’ve really put some effort into the engine as well as your writing about it! Fun to read and nice to see that you took it to the next level :thumb

    I think this article could even be used in the how to section. Ofcourse with your permission? And in due time, I’m quite busy with other things at the moment.

    I would really love to see some pictures of the inside of your cylinder showing the booster ports you made. The picture you used only shows a couple of mm’s of the top. As well as the windows you filled into your piston.

    Keep it up! It would be cool to read more about your future projects. It looks like you really catched the Vespa-tuning-virus so I guess this won’t be your last 😉


    Herr Flick
    Berichten: 6294

    Amazing project. It’s always nice to see so much effort put in to a ‘standard’ cylinder.

    For your next step, modifying the crankshaft, ArvidW made a really nice article how to measure the timing for that: click here

    Keep us posted!

    46 Pinasco, Malossi RV, Schijfrem, Fox Vario
    Gele Racefrikandel

    Berichten: 3386

    Dit yall crazy 2stroke boys know that the carbon on the top of the piston helps the piston cool ? Never polish it completely away just leave a bit on there

    At sew bass i like the mods a lot, my first cinder had also the ports not semetrical it dit run great any way

    De budget beun tjoener: geen geld is te duur of het werkt nog niet
    Link naar Mijn collectie / Projecten.

    Berichten: 2177

    @ritze, I’d like to see some well founded/proven arguments for that. I believe carbon build up would never have positive benefits.


    Berichten: 3463

    Very nice article, interesting and fun to read.

    A small note from my side, as far as i remember the spray bar from the 13/13 is different then the stock one, so just filing a stock one might not give the same results.

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