I haven't been able to get my browser to find this particular page - always do have problems and most times have to trawl through the items, but I'll have a stab at this one.
If the frame looks pretty classy, maybe lugless, might have a very wild artistic modern art spray job, looks quite mean etc it is probably a product of a small fairly dynamic company situated in a pretty village just off the banks of the Loire , near Tours, in central France - St Cyr -sur-Loire, if my memory is working well this morning. The company was a small distributor og high-end accessories, but also did a range of exquisite frames and - a speciality, racing tandems, often track versions. They have a record of sponsoring leading amateur teams and on one occasion sponsored one of the smaller Belgian trade teams for a short while.
I doubt whether Carlos.. and that name has no resemblance whatsoever with the name of the owner - but it sounds sufficiently exotic to sell frames - built the frames themselves. From what I recall of the company and the area around Tours, there were several excellent frame-builders available "on tap" so to speak. My money would be on a builder called "Phillippe" - I think that is his real surname, who has a good quality workshop in Orleans. He used to build for quite a few "Names" around the area and is still turning out some very very high class frames in aluminium alloy - very much a modern day Herse, but generally only racing frames. I think he had a hand in building those superb blue enamelled frames for Cyrille Guimard's team Maxi-Sports in the late 80/early 90s (Sorry that is off the List)
The other possibility would be Meral, a small high class builder at Aubuigne-Racan about 30 kms down river. Meral used to build "series" frames that fitted somewhere in between the custom-builder and the larger manufacturers, but would do "one-offs" Meral tried to break into the big-time in the 80s by sponsoring a Pro team, the first RMO one I think, but went into liquidation not long after, but the failure had little to do with the pro team or the bikes. When Meral went down, it left about 17 frame-builders out of work. Some moved away to anther Meral factory to weld up hospital bed frames but one guy, Dennis Quillon, stopped in the area, set up his own small business as a sub-contractor,,,and flourished. His work can be seen around the world with names such as Geliano, Rozelli ,J-P Duret etc all brands of a distributor near Gien not far away. At one time in the beautiful lake-side town of Annecy in the Savoie Alpes of France, there were thre lightweight dealers all selling high-end frames. All the frames bearing different names eg Geliano etc were made by Quillon and dsitributed by Duret. Quillon rode out the competition from imported products and then having flourished , expanded until he founded CYFAC in recent years. Such was the success of CYFAC that one of the big names in France, LOOK, or VITUS (possibly the same ownership now..) bought out CYFAC... and now Dennis does nothing but advise. and go to meetings... and be consulted.
I think there is a CYFAC on USA Ebay at the moment. Fantastic workmanship.
Domwwhere in the above ramblings and chatter you have the origin of the CARLOS frame.. assuming that it is the French CARLOS.. but I don't know of any other.
Norris Lockley.. Settle UK