Livefish

Bargo68, the unusual stamped number is unlikely to be of much help. I'm afraid my knowledge of the Criterium model is pretty thin and surviving published materials from Motobècane for it are also scarce. This bike could possibly be from 1972-73 as you're thinking but I'm guessing perhaps a few years earlier. It clearly was equipped originally with a Huret Allvit groupset (very popular in the 60s) with the Campagnolo Nuovo Record rear mech added later. The components in your photos were all being used in the late '60s. A 1966 brochure shows the Criterium in Reynolds 531 (likely 3 main tubes), half chromed fork, Weinmann 999s with light hoods, tubular rims, etc. and with a Brooks B15 saddle. In the 1966 brochure it lists a TA crankset and Pivo stem so your bike might also be a year or two different.

Great bike. In what country did you find it?

bargo68 

Thanks for the help! Agreed, the information online is also very scarce. This is the one page that has really helped so far:

It is from a 1973 catalog and there are a few discrepancies between it and my bike: different crankset and brakes being the most notable. But it's the closest I've found to a match.
Oh well, let's just chalk it up to the wonderful mysteries of French bicycle production.
And I found the bike on Craigslist from a posting in Walnut Creek, a suburb in the bay area of California. Walnut Creek is the home of Rivendell bicycles, if you're familiar, and the gentleman who sold it to me had a pair of Rivendells and quite a few other nice items of local interest. He had a couple frames custom built in Japan and sold in a Berkeley store called Jitensha that were beautiful!

DeathForks

yep, the serial number on my Motobecane Mixte is......1750022 with a little Y33 after it at an angle. This is on the rear left dropout.

Pictures to follow when i post uh... 8 more posts i think!

VintageSteelEU

It looks the saddle is original to the bicycle then. Not sure what they were thinking
I guess if you have Huret dropouts and Huret RD hanger, you might as well go Jubilee route. Here's a FD and here the rear one. This one is in the UK, but looks like it's for a Huret standard hanger and it's probably still cheaper than the cheapest one I've seen on eBay US. And looks decent. You could look for a late 70's model with Campagnolo adapter plate, D'Israeli gears mention it might work with an old Huret dropout after removing that plate and it may well be the case.
Plenty of Mafac Racers on eBay as well. Not sure if they are any better than Weinmann Veinqueur. Never used Racers, very happy with Vainqueurs. Mafac are probably lighter, but I also preferred the design of the Weinmann ones (I like the idea of recessed head of the centre bolt as well as shorter springs pressing against protrusions on the arms as opposed on the brake pad mounting nut).

DeathForks

I have many sets of Mafac Racers, I can't really attest to how well they work, but i find they have a lot more adjustment to where you can put the pads, and they just have a really cool look to them. I'm saving a pair for a Peugeot PX-10 I'm building up now

hdgurl

I have a black and red 27" frame Motobecane. I believe it to be a 1978 but could be a 1977. The serial number on the bottom between the pedals is 6182208 I believe.
Can you tell me anything about this bike based on the information I have given please?

non-fixie 

1978 sounds about right. Have a look here as well: Motobecane Serial Number Database

There may be other codes, on the dropouts and the steerer, that may or may not reveal more information.