1978 Motobecane Mobylette 50VLA

This is a 1978 Motobecane Mobylette 50VLA. It came with a 50cc AV7 engine. It’s yet another moped I got at an estate sale auction. My max bid was $225 but I ended up winning it for $190. The frame, chrome, seat and most parts were all in great shape. I only wanted to modify the engine on this one. This was my first French bike and my first variated bike.

Obligatory day of purchase photo:

This moped was in great condition when I got it but it was pretty dirty. I think I took the engine off and disassembled it before I even washed the bike. This has an AV7 engine so the only thing in the case is the crank and bearings. The transmission is made up of pulleys and a variator on the outside of the case. The flywheel is also exposed on the outside of the cases unlike my other bikes.

Engine disassemble wasn’t too bad. The bearings were shot but otherwise everything was in good shape.

I polished the cases up a little bit and put a parts order in. The first order: VM18, MLM Intake, Doppler Engine Spring, ER3 Variator, Artek K1 Crank, Bearings/Seals/Gaskets, Airsal 70cc Kit, Airsal 45mm Head, Doppler StreetCup Exhaust and a Le Partie CDI.

While waiting for my order I decided to clean the gas tank since I knew it had rust in it. I took out the petcock and put in an M10 1.0 bolt with an oil plug gasket from Autozone. Then I washed out the tank with simple green and a brush that attaches to my drill on a long snake. After I let it dry I poured in a gallon of Evaporust and let it sit about 18 hours. Then I drained that into a bucket and cleaned again with the Simple Green and brush. TONS of rust came out the bottom. I dried it again and filled it back up with the same bucket of Evaporust.

The frame felt solid though, no pin holes so it ended up cleaning up fine.

Engine Assembly Next:

You can’t use the stock center stand with the Doppler spring so I decided to modify mine. It was a bad idea. I cut the center out which made it way too weak and it basically bent in half. Eventually I made a custom spring mount for the Doppler Spring. It was shorter so it gave the stock center stand room to work.

The only problem was you had to tune differently because that changed the geometry of the engine swing. I had to put a much lighter spring in with my custom mount.

I didn't want to use the mounting bracket that came with the Doppler Exhaust since it is meant for the square tube swing arm. I decided to weld one together using some scrap metal in my garage.

The Doppler Street Cup exhaust has TWO restrictors on it. One is easy to find you just pop the metal blank out of the coupler. The other is inside the silencer so you have to take it apart. Then you have to grind off the welds and pull out the tube looking thing. I could only go about 10-15mph with this setup and the restrictors in. When I took them out I was instantly going 45mph.

I also painted the exhaust bracket black.

When you have the non-clutch pulley ER3 you have to do something called the “cardboard trick” to start it. This involves taking off the belt, pulling the cheeks forward, sticking a piece of cardboard in and putting the belt back on. Then when you pedal-start the moped the cardboard flies out and hits you in the eye.

The solve for this is to get a pull start. Finding one is next to impossible because they are not mass produced. When you can find one they are over $150. I decided to design my own pull start and 3D print it. First I made the white one to test dimensions and proof of concept. It was some piece of scrap plastic I had in the shop, teflon maybe? I don’t know.

Mine used an ER3 nut with a hole drilled in it. You attached the pull start to the nut with a barrel bolt and then use the nut to put the CDI on.

It worked great but my printer uses resin so it was too fragile. With a stronger print this would be a pretty perfect, LOW BUDGET pull start.

WARNING GRAPHIC CONTENT AHEAD!!!

I mentioned earlier that the transmission is basically exposed on these French bikes. The variator is spinning at thousands of RPM only inches away from your feet as you ride. I ended up getting clipped by it one day, ouch. I’m putting the story on here because someone reported the photos of my leg on Instagram and the post got removed. Thanks nerds!

So one day I was tuning this bike in my shop. I had a lot of problems with high temps on this bike so I was always doing things to try to lower them. I used cooler spark plugs, domed out the head more to lower compression, retarded the timing as far as possible, upjetted, everything I could think of.

I had just done some adjusting on the carb and put it back on. I started the moped in the garage on the concrete floor. It was revving super high for some reason but my weight on the moped on the concrete kept the bike in place. Like, it was revving high but it wasn’t accelerating. I thought it would be fine so I wanted to at least take it up and down the driveway.

As soon as I pulled out of the garage onto the stone driveway, the back wheel broke loose and started fish tailing. For some reason I just put my feet down and held the brakes. The back brake wasn’t holding but the front was so the bike just fish tailed in between my legs and swung right into my left leg.

It literally knocked me off my feet and back onto the seat and I rode about 100 feet down the drive way before I killed it and came to a stop. I was wearing boots and heavy pants so I didn’t think I was injured. I was still sitting on the moped as I bent down and lifted my pant leg. My sock was already soaked with blood.

I didn’t peel it back I just squeezed my leg and tried to call my closest neighbor. Then my closest relative. Then my other closest relative, Lol. That ended up being my sister and she was about 15 minutes away. I knew I needed to go to the hospital. I also knew I better not pass out so I just stayed there, leaning over the bike holding my wound shut.

Eventually I tipped the bike over so I could sit in the driveway. I started to group text some friends to lighten the mood and stay calm. That is why I have these photos, LOL. I asked if I should peel my sock down and look at it and both my friends said yes. CAUTION DON’T LOOK AT THE PHOTOS IF YOU DON’T WANT TO SEE MY SHIN BONE:

That chunk of flesh was gone. I ended up getting 20 stitches, basically in a circle around the hole.

After that happened I didn’t really want to ride it anymore. I ended up selling it to someone from Michigan, I think? I can’t remember. It was definitely a beautiful/fast bike though!