Inside the beast

Rebuilt engine after full checkup:

Engine rubber mounting conversion Phase 1 + a peek at the Mykitech cases/minarelli scooter 86cc on the peugeot 103 frame for the big bore fans. Why not? My race bike with a modified chassis would be a good candidate to test that kind of power + launch lever. But with 25hp I would probably install my better Paioli 30mm adjustable hydraulic fork + steering damper.


Here’s an exclusive look inside the engine of my Peugeot 103 RCX 50cc race moped 14hp converted back to a street moped without the race fairings. Before riding the bike on the streets I need to do a complete engine checkup after 5 races on the track.

The engine is a 49.9cc Bidalot h20 kit replica (with transfer ports smaller than a real vintage Bidalot racing kit) + graphite AGP piston + Malossi cases + Bidalot crank 16mm, Pvl analog cdi, Dell’orto 21 carb, Giannelli pipe, steel Bidalot variator and Giraudo clutch pulley. The engine was built by Remi Cusso french master tuner with 20+ years experience in moped racing. As you can see nothing crazy there just a very nice job on the exhaust porting and the malossi cases barely ported with minimal aluminum removed to match the Bidalot cylinder ports. Special crank lubricating holes added to the cases and guides inside each half for a perfect alignment. Guide also added to the h20 head for perfect alignment with the cylinder. Some good “race shit”… you do it right or you don’t do it.

QUICK TIP: The real power of 2 stroke small moped engines doesn’t come from porting the shit out of the cylinder and cases or using gigantic bore, carb or intake, but from properly assembling the engine very slowly, using metrology (the science of measurement) and paying attention to every single detail like a surgeon. Also knowing for each cylinder kit what swept volume and transfers + exhaust port duration works best with what cases volume, intake size, carb size, pipe size, rpms, ignition timing, spark plug, combustion chamber volume, squish with fuel octane rating, final transmission. Some extra horsepower on mopeds can be gained or at least not lost with a light chassis, zero resistance for spinning parts or brakes, good lubrication and alignment, tire pressure, engine proper cooling system, aerodynamic fairings, vegetarian diet plan… lol, etc…

Once I got the motor back in the US, I built a custom rubber mounted engine spring, laser cut some guides for the vintage Bidalot variator 100mm, completed the engine with all the h20 system and spent a lot of time in 2011 tuning it with the right timing + carb settings + pipe length + launch lever + variator weights + transmission for the race track in Southern California but no moped racer 50cc or even 75cc showed up to challenge me. I’ll wait next April 2012 to race against 200cc motorized bicycles. I wonder what’s next, Harley 1200cc engines? I’m really curious to see where it’s gonna stop with bigger bore engines in the quest for power? Isn’t 49.9cc the real limit to call it moped racing, and tuning skills to make the engine faster the real fun challenge? Or functioning pedals makes anything a legit moped no matter what the engine size?

5am in the morning, let’s do this:

Engine dismount, taking note of all the settings before taking it apart, timing, squish, checking the compression, piston ring gap, nikasil at top deck, crank bearings + seals, rod, needle cage bearing,  piston pin, viton O-ring, variator full checkup with new guide allen screws for every race, weights arms pins, carbon petals reeds, engine spring, water hoses, etc, etc…

If I’m not too lazy and have enough time I should weld and install some motobecane rubber bushings. The engine is half way rubber mounted with the custom engine spring but I need to finish the job to get rid of all the vibrations causing the exhaust springs to break at high rpms. It’s a little complicated because I need to make sure that the variator stays perfectly aligned with the pulley to avoid any problem with the belt, there’s no room for error when you’re dealing with a race engine.

Quick note:

The piston’s head shows a perfect gas flow and no overheating as a  result of a good exhaust porting job. The Bidalot high quality needle cage bearing is recognizable by its blueish color. The multiple new base gaskets worked fine instead of an aluminum raiser not available at the time. The crank shifted a little off center inside the cases probably due to the heat at high rpms on the track but no worries there everything feels tight. To protect the engine I kept the carburetion rich and like all the moped racers in France I’ve been using some (hard to buy) airplane leaded Avgas 100LL  fuel rich compared to the dry unleaded 91 or even 93 octane fuel that we normally get at a gas station. Next year I’ll try to get some leaded VP C12 racing fuel octane 108 with appropriate cylinder head squish.

Disassembling an engine after few races is important to prevent any mechanic failure or horsepower loss, and gives a good reference point on the parts wear after a certain amount of miles or time spent on the track, it helps with scheduling the next checkup.

Time to change the piston ring to regain between 1 to 2 hp.  After measuring the ring gap I can now evaluate how fast a new ring wears and know that it won’t last more than 2 or 3 races with full power before replacing it.  I measured the transfers and exhaust port duration in degrees set with pretty high numbers based on Gr2 specs but close to Gr3.

That engine looks really clean after 5 races and stayed reliable because of a conservative porting and restricted rpms taking no chance to break the 16mm peugeot crankshaft also very thin on the variator side. A 2 stroke race engine performs at its BEST when pushed to the very limits (high rpms, small squish, compression ratio, leanest fuel mixture, etc…) but then can fail at anytime and make you lose the race,  it’s like a “catch 22”. To win races, you have to compromise but also adjust after each race and make changes according to your competition on the track. Sometimes it takes an entire season and if your fellow racers are not 100% dedicated or don’t show up the following season then you’ve almost tuned your bike and pushed the engine limits for nothing.

So… you still want to be a moped racer?

Peugeot Malossi cases and Bidalot 50cc h20 kit available at

Hmmm… Check out that vintage full Bidalot kit party 50cc air cooled 15 carb 11hp bolt on, for 80’s 90’s Peugeot Gr1 class entry level moped racing. I wish they’d still make those racing parts instead of  those street replica parts we’re only getting now.


Moped racing in Oregon. I got the photos from facebook Lara Burke’s album thanks to Jeffrey Jay Herzog moped racer with the polini 70cc black motobecane av10 #22. Why doesn’t this happen in California anymore? I’m sooooo jealous. It seems like they get 6 to 7 consistent riders and 10+ on a good weekend. I may have to save money and drive all the way up north once or twice a year to have fun with those fellow racers. Jeffrey is building a new engine for his black moby next year based on my Gr1 50cc setup and also building 2 or 3 extra loaner bikes for anybody who would want to try moped racing in 2012.


France, Team Remi Cusso vintage Bidalot RS 50cc race moped in action beating the modern Japanese, Italian, Spanish 50cc 6 speeds race bikes during an open practice round in the south of France Championship 1st race of the 2011 season last April. I was actually at the race and witnessed the power of those 50cc 18hp mopeds, it was so impressive. The “old pops” technology stunned the new kids and proved that 50cc variated race mopeds are not dead and still kicking ass.

On board video with a rare camera angle mounted on the swing arm at the bottom of the shock. Old school Moto GP style:


ALSO… from the early 90’s in the peak of french moped racing era, vintage photos of a variated 50cc race moped prototype chassis GR3 (no carb size limit class) built by an independent french team that later became the official bike of  the Ninja exhaust company team:

PLUS… Peugeot 103 race moped winner of the 2011 South of France championship season in the entry level “stockish factory” class, stock 50cc air cooled (ported), stock cases, 15 carb max, performance exhaust, stock variator.


AND… treasures of G3 Raptor’s cave (french builder and racer) hidden somewhere outside Paris. Bidalot Gr3 clutch pulleys, engine springs, intake manifolds, cdis.


  1. Neil

    Hey Chris
    Here’s to tons of Moped racers at the track on Sat April 7th 2012
    or maybe it’s time to build a Motorized Bicycle racer?

    Would like to come to visit you at your new shop in Anaheim.

    Talk to you soon buddy ,,,,,,


  2. tomahawktuning

    I personally don’t expect any moped racer at all.
    It probably will be just me and maybe few friends to watch my moped racing against the motorized bicycles.
    I won’t have time to build a bicycle. It’s ok, they welcome my 50cc moped and we’ll be able to see if some of those bikes made any progress since the last race…. I’m kinda like the “rabbit”.

    I’m setting the shop in Anaheim in January and not there every day but let me know when you come visit.

  3. Pingback: another tomahawk « pedShow

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