Motobecanes are peculiar little creatures. Definitely the most spirited mopeds I've ever worked on. They can vary 10 mph in top speed from day to day depending on how they feel, and go from starting in one kick to frustrating you to the point of tearing your hair out, over night. While it is important, as with any moped, to maintain positive energy and respect the moped's spiritual soverignty, there are a few modifications which, when done correctly, will greatly increase the chance of him/her starting predictably. When done properly, these improvements will not upset your Motobecane, rather will strengthen your bond and make your moby a happier little animal.
To start with, any venture into moby-land is incomplete without a visit to Mabecane's Mobylette page. The virtual proprietor, MaBecane, is one of the most interesting people involved in mopeds. He loves these bikes like children, and shows an unmatched zeal for historical preservation, caretaking, and helping others keep their mobies running long after it makes sense. Check it out here for tons of info and pictures to get you excited about your build: MaBecanerie Also, grab a manual while your at it. The manual is a poor copy/translation, but the verbiage is really pretty, in french style. Lots of adjectives to fully illustrate the tenderness that is inherent to motobecane repair.
Esti (above) is a good friend and former neighbor of mine, she is a perfect candidate for a moped rider, and since riding some bikes when I moved in underneath her, she's been looking for a 'yellow moped.' Not many bikes came in yellow, but i knew of one brand that did, and a Motobecane was a perfect fit for her classy style. I found this 1976 50v in a friend's storage unit, in pretty good shape, completely covered in black greasy grime. The grease protected the paint and chrome, and whoever had it last managed to avoid bodging much besides the carb, seat, controls, and electrical. The cylinder was tight, had good compression, and all the important stuff was there. This is pretty typical of a 'barn' or garage find moped, so I'll go over the common problem areas and detail the repairs and modifications I made to her bike, so a novice could get her feet wet with a reliable and fast machine as she learns the ropes.
Most barn/garage rescued Mobies will have all the cables frozen on them. For some reason the grey cable they used cracks and rusts out like nobody's business. The motobecane uses knarps on everything, though, so you can pick up a full mountain bike cable pack at your local wal-mart, for $7 and cut all your own cables to fit. If you want to get crazy, and replace everything with OE grey cable, you can talk to my friend Matt Quirk, at Motorwest Motorcycles in milwaukee to get a roll of the grey stuff in much higher quality than Motobecane ever intended.
At the very least you'll need new throttle, front brake, rear brake, and possibly decompression. Choke depends on the carb you use.
Speaking of that carb... Motobecanes are notorious for the Gurtner carb. Many moby fanatics will tell you they can go 50 mph on the stock gurtner (i've seen it..). For someone who wants to eat, sleep and breath french, the gurtner is a perfectly workable unit. For most of us however, its much cheaper and easier in the long run to just swap out to a generic Dellorto SHA. You loose the extra cable of the choke, you get standard replaceable jets, air filters, a bigger throttle, and they are less likely to leak with the rubber-tipped float needle. You can use either the real-deal SHA 13 (vespa style), or the Spaco clone (kinetic), or go to a standard 14 SHA or 14 SHA clone (my favorite). The clones might have some issues with changing jets, but if you're hardcore and used to making weird stuff work, you already have a set of JET DRILLS to fix that. In addition to your fuel system woes, the stock petcock is almost invariably broken or leaky. Quarterkick.com seems to have these in stock more often than the other guys, so give Chad Burke a try first. If they aren't on the website, they might still be in stock.
The Motobecane AV7 (50v, 40t, 7, traveler) comes with either a long bendy intake, or a short stubby intake. The stubby intake is actually too small to easily mount a SHA carb (apparently with a little fin grindage the 13SHA fits), but either way, its much easier to just buy the Malossi SHA intake for av7, which is available dirt cheap from the major moped parts sellers.
I've heard some nightmares about Moby Electrical, in fact the first two mopeds I ever owned were mobies left outside for many years, and were hopeless, the coils were all rusted to hell. For most motobecanes in fairly good condition, the coils, condenser, and points are inside the flywheel and fairly well protected. The problem areas with moby electrical are the questionable connectors, namely the white plug thingy under the floor boards, the coil, and the incredibly awful spark plug wire.
The terminals of concern are the white ones under the floorboards. The prongs in them are very small and flimsy and prone to corrosion between the terminals themselves (easy) or between the terminal and the wire (very hard to diagnose) they also have a nasty habit of popping the terminal itself out of the white plastic housing, making it look connected when it isnt. If they look good, hose some dielectric grease in there and forget it. If they are really shot replace them with soldered or properly crimped on blade terminals.
The NOVI coils, white, strapped to the bottom of the tank, are prone to cracking and rusting inside from what i can tell. The spark plug wire is a proprietary unit with compression style terminals, and an obscure 5mm diameter. I would strongly reccomend buying the 'universal moped coil' that the major moped retailers have for sale. It uses a standard 6mm wire with screw post, seems to deliver an incredibly strong spark, and is all zinc plated and epoxy potted for long life. It grounds through the frame so the coil wire should work fine. Everything should be a very simple plug-and-play situation. You'll need two 5mm bolts to bolt it on. dont forget lock washers or nylock nuts. Set the point gap to stock, clean up the points, and you should be getting a nice fatty spark.
For performance stuff, you probably wont need much if you have the 'fast' 30 mph cylinder. They fly pretty well out of the box. Upper 30's with a 14SHA means everything is solid. If not, your timing, bearings, variator belt, or brakes might be at fault, or you have one of the slower cylinders (or your exhaust is plugged, but this doesn't seem to be much of a problem for moby). The only differences between the two is porting. I wont go into it in detail because there is much better info out there, but lowering the intake about 1mm, widening it 1mm on each side, raising the exhaust about 1.5 mm and widening it about .5 mm on each side with a nice radius up to the top, should get you close to the stock fast cylinder specs. It might be easier to take the engine off if you are going through this much work.
Yep yep, so thats about it. Moby refresher in a nutshell. The first time that thing pops to life, you will understand the beautiful feeling. They whirr, they rattle, they glow, they are strange little beasts, but when properly set up they can be amazingly reliable and a real pleasure to ride for many miles. Once you have your bike running and solid, you may also need to replace the rubber engine mounts (which i'll cover in another post sometime) or do some of the other basic tuneup things such as bearings and brakes, which are similar to the Puch demonstrations i'll post up here soon.