I’m never going back to 70cc kits at least with french variated mopeds, ever! Less power with reduced port duration, overheating with bigger piston head and more vibrations to brake your engine parts, bad combo.

Motobecane av10 mopeds are so fast with small stock cases and a good 50cc kit slightly ported. I have to do so much more work on 50cc peugeot bikes though to get that kind of power, even though on paper it should be faster using a “square engine”. It must be the stroke that makes the difference on motobecane bikes. Now I understand why motobecane race bikes ruled french moped racing for more than 30 years and peugeot bikes ruled the streets with custom tuning.

I’m glad I did a bunch of research and stuck with 50cc engines for the past 2 years to take my tuning skills to the next level. When you want to increase the power of your 2 stroke moped engine you should learn the basics of tuning  first and find out how to get the most power out of your 50cc engine. Choosing the “bigger bore” route is not necessarily the right approach if you don’t have the tuning skills yet, you’ll never learn. It takes time, research and hours of testing but once you’ve mastered 50cc 2 stroke tuning you can apply the same formula to 70cc or 80cc kits for insane power. The problem with mopeds or even scooters sometimes is to find a crank that can last and take such power at high rpms. Also remember that the key element hard to master in 2 stroke tuning is the final touch, the pipe!

I did a quick test run at night with a Doppler clutch pulley that I modified to make it more heavy duty than the weak stock version + a smaller rear 52T sprocket. The idle is a little high, the Doppler stock springs makes the clutch 3 shoes grab a little late but the power is insane! The bike has super fast take offs and keeps pulling even with the small sprocket even though it toned down the engine a little. There’s still room to increase the rpms by modifying the pipe but I prefer to keep the engine reliable. With better wheels and tires I honestly believe, after competing in 2010 against the fastest 75cc mopeds and watching videos of other moped races, that right now that bike or my other fast Peugeot 103 rcx 50cc h20 would be hard to beat. I’ll keep the cheaper to maintain motobecane for street racing and the more expansive high tech peugeot for the race track.

The bike is so much fun to ride now with power everywhere, fast take offs, crazy acceleration and top speed. It’s scooter fast now but with better top speed, scooter type dual variated transmissions absorb some of the engine’s power, they rev high but don’t pull like a single variated bike and don’t make you feel that kick when the engine hits the pipe at maximum power. It makes me want to keep the clutch pulley even if I have to take it off after almost each ride to keep an eye on the one way bearing that tends to brake if not lubricated often. I can’t wait to get one of those new prototype heavy duty clutch pulleys that I’m working on with an engineer in France and that are being tested taking a beating on the track to fit on peugeot and motobecane street bikes. I hope to be able to manufacture and import them very soon.

Cut off pedal to hold the pulley                             Exhaust safety brake cables

Bonus pics: Entry level 2008 motobecane av10 Bidalot 50cc air cooled Gr1 french race moped.

Special thanks to my friend Remi master tuner from France with 20+ years of experience in 50cc moped racing who guided me in my quest for 50cc power.

Pics of his first Motobecane av10 Gr2 Bidalot 50cc race bike (high mount exhaust) 23 years ago blasting the streets of Paris at 75 mph and his top level Bidalot Replica Gr3 50cc race bike currently competing in the french 50cc variated championship.

1- Test run with Doppler Er2 clutch pulley.

The acceleration lifts the front end and you can feel the pulling force. I need to buy a steering damper just like the race bike above asap!

Man… that test run reminded me of the early 90’s when we used to race our mopeds, scooters, motorcycles, cars every Friday night in the streets just outside East of Paris on the Esplanade de Vincennes plaza just behind the castle located in a big park. Hundreds of crazy machines, latest technology, stolen bikes, loud engines, burn outs, smoke, fast runs, leathers, hot dogs, alcohol, prostitutes, cops, etc… It’s gone now.

I’ll never be late for work with that bike!

Another test run with the same Doppler clutch. Very good acceleration but I’m already having problems with the one way bearing.

Next test runs with adjustable Mykitech scooter clutch 3 shoes and vintage RGD/Bidalot clutch no one way bearing with special 2 shoes dual function to start the bike…

2- Test run with Mykitech clutch pulley:

It took me a while to tune the Mykitech clutch. It feels very heavy and the springs are way to hard making the shoes grab super late. My 50cc engine was screaming and I could barely take off. The shoes feel light and seem to start a little too far from the TGB clutch bell. That clutch pulley was definitely made for the race track with super high rpms screaming engines like a motobecane 50cc Gr3 moped or a ported 80cc minarelli scooter kit with the Mykitech cases designed to mount on moped frames.

The winning ticket is to use the softer Doppler stock springs and adjust the tension according to your engine’s power and rpms. Even with my 11,500 rpm engine the shoes still grab a little late and too smoothly compared to the Doppler clutch. Good thing I’m a using a launch lever to compensate and find the sweet spot to make that clutch work. I lost some the violent acceleration but that clutch definitely feels more heavy duty than the Doppler, no problem with the one way bearing that fits tighter on the shaft. But that being said, it would have to be tested over time doing a lot of stop and go in the city which wears out the one way bearing faster than on the race track being used mostly at the starting lane. Overall I don’t recommend that clutch for street riding but should work fine on the track.

I think I’m going to go back up 2 teeth with 11 x 54T rear sprocket for the next test run with the vintage RGD clutch pulley. It should the perfect transmission with the engine’s high rpms for street riding with quick accelerations and fast top speed.

I hate doing test runs in traffic.

3- Test run with vintage RGD clutch pulley.

I really like that clutch but it’s only a copy of the Bidalot clutch pulley and doesn’t come with adjustable weights on the 2 shoes. I only have one set of springs so I can’t tune it yet. The good thing about that clutch is that it doesn’t use a one way bearing and allows you use any front sprocket from 10T to 13T, unlike the other pulleys that come with a machined shaft with 11T sprocket. That’s “race shit”…

I took a couple of runs to get used to it, learning the transition between the starting function pads and the clutch function pads. I couldn’t fully test it because I still need to machine and replace the damaged pins that rubbed against the steel bell, probably after taking a beating on the french race tracks and probably not being assembled right. I can hear a clutch metallic sound so I may need to add extra washers inside. I’ll ask Remi about that noise since he’s used the Bidalot racing version for years.

I really had to press hard on the launch lever and make my engine scream to get the full potential of that clutch but I had to ease off because it was on a hot day using a air cooled engine. It’s definitely another clutch designed for the race track and very high rpms engines but once I can tune it for street riding it should be good.

After testing those 3 different clutch pulleys, the Doppler one feels the best for street riding. Too bad it has a cheap bell that heats up, doesn’t come with heavy duty pins + triangle brace and that half of the models have problems with the one way bearing under extreme power. It’s time to manufacture an improved version of the Doppler pulley or start from scratch with a regular 2 way bearing and maybe a kick start just like on the 90’s stock motobecane av10 50cc h20 version.

Street riding URT clutch pulleys 15mm shoes for peugeot 103 and motobecane av10 + racing Bidalot adjustable clutch pulley 25mm shoes for motobecane race bikes (like my RGD).

RDG clutch pulley test run.

Until I can find the perfect clutch pulley for street riding I’m switching back to a standard pulley with no clutch. I don’t have to worry about bearing and shoe pads wear or being stock on the side of the road. I did a final test ride with the standard pulley and 11 x 54T rear sprocket. As I anticipated, this is the perfect transmission with my “low” 11,500 rmps 50cc gr1 engine for quick acceleration and 70+ mph top speed. I actually regained a more direct and violent acceleration than with any of the 3 clutch pulleys I tested. It feels less like a scooter and it’s slower of the line like a one speed Puch but faster once the engine hits the pipe, it’s scary.

There’s nothing like blasting down Hollywood Blvd at night for a quick test run.

I think I’m done for a while with speed, tuning and testing fast french 50cc variated race mopeds. I’m gonna concentrate on finishing my peugeot 103 streetfighter and the motobecane 40T project. After that I want to explore stock Tomos Sprint mopeds and convert them into nice top tank bikes 45 mph.


  1. Eric

    what are the exhaust safety brake cables for? also, is that exhaust bracket custom? having trouble with my ninja ball joint loosening.

  2. tomahawktuning

    The exhaust cables are part of the safety rules in french moped racing.
    When the springs break under high vibrations the cables prevent the exhaust from dropping on the track and create an accident. You should do the same with the rear exhaust bracket.
    It’s good to have them for street riding as well. If you don’t carry extra springs in your back pack you can always manage to ride back home slowly.

    For loose threaded ball joint use some high temp silicone sealant.

  3. teamneal

    so I have been religiously following your blog and really like what you are doing. I am also building an av10 with polini race cases and 50cc h2o polini cylinder. But alas, I am stuck because I cannot find any motobecane engine building specs. I was wondering if you could offer any advice as to where i could find that information. thanks in advance…..

    Team Neal

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