A Mobylette, for the uninitiated, is France’s idea of motorised transport for people who aren’t in a hurry. A sort of halfway house between a bicycle and a moped, powered by a tiny two stroke engine that only bothers to run once you’ve pedalled hard enough to shame it into waking up. In motorcycling terms, it’s the two wheeled equivalent of the Citroen 2CV: slow, charming, mechanically simple, and determined to keep going no matter how much dignity it costs you. They were everywhere in the early 70s, buzzing through French villages like caffeinated wasps, beloved by teenagers, pensioners, and people who didn’t mind arriving eventually.
And I’ve spent the last month trying to resurrect mine.
The trouble actually began last year, when the original M4 thread holding the tower cap finally gave up. It stripped itself clean out of the carb body, leaving the cap wobbling like a loose tooth. The result was predictable: air leaks, fuel starvation, and an engine that would only run if I held the cap down with one hand while pedalling with the other, like a circus act devised by someone who disliked me personally. I promptly relegated the whole machine to the bike shed, where it sat in quiet disgrace until I had the time and the willpower to tackle it.
Complicating matters is that I am not entirely sure what Mobylette I actually own. Motobecane delighted in producing endless variants, subvariants, transitional models, and revisions of revisions. Mine appears to be a cross between at least two of them, and even one of those underwent several engine updates. Trying to identify it feels like conducting genealogy for farm equipment. Which is why sourcing an exact replacement carburettor is an exercise in futility – I can’t order one for “the correct model” when I haven’t the faintest idea what that model is. And even if I found one, it wouldn’t be original unless I nicked it from another Mobylette.
At some point I even replaced the original single seat with a double, on the optimistic premise that Hay might want to accompany me on a gentle jaunt – provided, of course, that there are no intervening hills. Some Mobylettes did come with double seats as standard, but that was a triumph of hope over physics. The poor thing struggles with me on board; add a second passenger and you might as well walk.
The ergonomics are, naturally, all wrong with the double seat - you're much closer to the pedals, which makes peddling from a seated position impossible; you have to stand to pedal and get it going, and then proceed down the road at 25 mph with your knees somewhere near your chin.
At that stage, the thought of drilling out the M4 filled me with dread. Aluminium is unforgiving. One slip and you’ve punched clean through. Yes, I could have used a Helicoil (or whatever the modern thread insert is called), but the idea of attacking a 50 year old French carburettor body with power tools felt like tempting fate. Hence the attempt at the simple solution: buy a replacement carburettor instead and avoid the drama entirely.
So I did. Thirty quid. Not Chinese. Utterly wrong. Back it went.
I tried again. Another thirty quid. This one was from China and, to my astonishment, looked absolutely perfect. Unfortunately, it arrived without the float, piston, or indeed any internal parts at all. A beautifully cast carburettor-shaped ornament. Refund obtained.
Which left me exactly where I had been a year earlier: staring at the original French carburettor, held together by nostalgia and the shredded remains of an M4 thread.
This is where the vagaries of the M designation come in. An M4 bolt is not 4 millimetres. An M5 bolt is not 5 millimetres. The number refers to the outer diameter including the thread. What appears to be a minor jump is actually quite a leap. And then you discover, usually after a small crisis, that the tapping size for M5 is 4.2 mm. The entire system seems designed to keep the uninitiated alert.
Before I could do anything, I had to find my tap and die set which, thanks to the Law of Garage Entropy (about which I’ve written before), had migrated to somewhere between ‘exactly where I left it’ and ‘the spirit realm’. After half an hour of rummaging, muttering, and finding tools I had forgotten I owned, I eventually located it wedged behind a box that definitely wasn’t there last week.
With no alternatives left, I took a deep breath, accepted my fate, and drilled the thing out. A clean 4.2 mm hole into the alloy, tap it to M5, and open the cap to a straight 5 mm so the bolt could pass through without complaint. There was just enough metal. Not an abundance. Just enough.
Cost of solution: £5.99 for a pack of M5 bolts.
Cost of carburettor-related optimism: £60 and two wasted orders.
With everything bolted together, I gave the pedals a shove. One and a half turns out on the mixture, and the Mobylette coughed, spluttered, then burst into life in its familiar peddle and pop fashion. It still won’t idle, choosing instead to stall like a French civil servant refusing to work after lunch, but that’s just a matter of tuning now. And honestly, it feels entirely true to the marque.
At least it’s original – which is more than can be said for many survivors of its age. Well, original apart from the M5 bolt that now holds the tower cap on, but that’s a minor mechanical enlightenment disguised as authenticity. These early 70s peddle and pop relics aren’t valuable enough to justify selling, which was the original plan. So instead, I’ll keep it a while longer and sling it on the back of the motorhome when we go on safari around Britain. If nothing else, it’ll give the locals something to point at.
So the moral is simple. You can buy two carbs for £30 each, discover neither is remotely usable, and still end up fixing the original with a £5.99 packet of bolts.
The Mobylette lives again. Badly, temperamentally, and without idling. But it lives.
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