RT325-  Favor please.  Can you take and post a photo of your AT1 engine number? 

I believe RT325 posted photos of his vin on post #17

Mark T if it will help I can get you some pictures of my AT’s if you want to compare the fonts

Thank you Lizeec!  I thought I saw it but could not find it!

RT325 AT1 ENGINE NUMBER

I'm no expert on VIN stampings, 1960Super10's engine and frame stampings do look legitimate to me.  They seem to have the unusual Yamaha fonts.  As Gr8uncleal pointed out, Japanese Domestic Models (JDM) usually do not have a serial number on the engine.  That said, RT325's AT1 that has a VIN beginning with "4" does have the complete VIN on the engine. So that means it's likely a export model...  but to where is the question?
imgur.com/dzfXozh
 

It's possible that it's an AT1C-MX?  If it is, I would say it's very likely to be a non-USA model.  It also could be a non-USA model that someone converted to a MX with Yamaha parts?  (And maybe the "rich kid" owner bought it from someone already converted?  Having a "rare" version like an import is often very attractive...  he would likely be the only one in town with a non-US example)

I have a copy of an old book that was/is used by Law Enforcement to verify USA motorcycle VIN numbers.  It shows the VIN ranges for different early model Yamahas, including "off road" and "motocross" models.  They show the AT1 MX models.  No AT VIN with a sequence beginning with "4" is shown. 

It's also possible that Yamaha did export some AT1M models to the US with a VIN beginning with "4"?  Maybe Enduronut will know for sure.  I'll send him a note and ask him to look at this thread.




 

A couple more thoughts... this "potential" AT1M appears to have an ignition switch of some kind? That's certainly not original to a US model MX. (which didn't have any kill switch at all!)

The other oddity is the neutral switch. Someone will hopefully correct me if I'm wrong but I remember the AT1M models having a neutral switch WITH the boot and "sky blue" wire connected. I don't remember seeing any full photos of the left side of the bike... my experience is that on AT1M's most people left the wiring as it left the factory... lighting coils, neutral switch wire, etc.

(Curious what the oil tank looks like too)

In my experience, when someone converted a magneto model to MX, that's when the tendency was to remove everything wiring related except the points wire to the ignition coil. It seemed logical that if you were removing the lights that you needed to remove the power source for the lights.

Again, none of the above are "conclusive proof" of anything... except someone has modified the bike. It's hard to know if it it started life as an "MX" and someone modified it slightly? Or if it was an Enduro and someone converted it to an MX?

Here are a few known answers for you. # 418229 came from the factory with no kill switch or ignition lock whatsoever. I added both of those in my trail bike conversion in 1975. The cleated pegs I always figured had been added by the original owner. I mentioned them earlier in case anyone here also had cleated pegs. I added photos of the front fender mount and the original alloy fender to show exactly how they looked. Right after I bought the bike, I had a mechanic change the sprockets and chain, rebore the cylinder, rejet the carb, and add the key lock and kill switch. He also reinstalled the oil pump, added the Skyway silencer and did whatever else it took to bring the machine back to life. I bought a replacement rear knobby a few months later that has never left my garage wall because I discovered that I was soon moving to a place far away from the trails an old college buddy of mine and I had made. That's why this machine has been a survivor with so few miles. The machines I especially like, I keep a long time!

A wild card idea that I have had is what if this machine has never been to CA? What if it was shipped directly through the Port of Houston and those machines had special numbers? I currently own a 2008 Toyota RAV4 of a similar case. The SUV came through Houston and has a couple of things significant to Houston RAV4's only.

A lot is possible!

One of the really common questions here is from someone that has a bike that doesn't fit into the VIN tables. Most turn out to be models that were originally destined for other countries. I simply can't recall any AT1M's like yours... I do remember an AT1 Enduro or two with different numbers that definitely were non-US models.

I did email Enduronut. If anyone has information about the "AT1-4XXXX" models it's likely him. Hopefully he'll take a look at this thread and respond.

And it really doesn't matter anyway... it's still a great bike!

P.S. Did you ever get a chance to check for a carb ID number?

The top of the carb mounting flange says 248 M2 E2 and it measures 26mm. There is also a 302 or 802 stamped just above the E2. That 3 or 8 is so feint that I am not certain if it just says 02 instead. Another clue I just found is that the throttle cable at the handlebar goes into a very simple assembly that was clearly never made to house a starter button. Another clue is that there is no bracket welded to the frame to attach the ignition switch, indicating the frame as definitely a 1971 model since the switch had been moved to between the instruments on the Enduro model.

I do not know how to do an ebay link here. If you go to ebay and search for YAMAHA MIKUNI GYT MX 248M2 VM 26mm RACE CARBURETOR 1969-1971 AT1-CT1 SPECTACULAR you will find a carb for $325 that is identical to mine in every way except mine has straight bolt openings in the flange. The ones on the ebay carb have an unusual upward curve, as if that carb is meant to fit multiple models.

A mystery indeed

Unfortunately, I don't have information on the 4xxxxx series bike, but I'm sure it's not a USA model
On the surface, it certainty looks like an MX, but that might be hard to prove without access to genuine Yamaha serial number records

I do see at least one part that should only be on the Enduro models, but bottom line is, anything (and/or everything) could have been changed since we don't have the original history of where it came from.

I would like to see a picture of the carb numbers, which do not make sense to me .... possibly has been re-stamped
The carb on eBay that you mentioned, has been modified by someone.

The 1971 AT1MX that I have here, has a 3xxxxx series number . . .  I've never seen one that started with a 4XXXXX
If my parts fiche and books are true, the MX model did not have a neutral switch on the engine case, Yamaha claims it had a bolt, or what they called a blind/straight plug (part # 90340-20004)

The MX & Enduro model shared the same throttle housing ... the elec. start switch was held in place with a tiny screw