Hi, guys. I just found this site and joined up. I have owned a 1971 AT-1CMX survivor for 48 years. I am also the author of The Tiddler Invasion (look it up on Amazon). I have been researching facts about my machine recently, as well as related first generation Yamaha Enduros of all types. At a quick glance at some of the material on this site, I have noticed a few discrepancies enthusiasts of these machines might like to know. (1) Someone somewhere posted on the net that all AT-1CMX serial numbers began with a 3. This is absolutely not true. My machine is # 418229 and I have found at least one other identical model with # 419614. (2) The AT-!C had 3.00 and 3.25 18-inch wheels, but the factory MX model had 3.25 and 3.50 wheels. (3) I have not specifically seen this on this website, but most online spec charts miss the fact that the AT-1CMX has a close ratio gearbox not shared with the regular AT-1, GYT or otherwise. I hope this information is helpful to you. Thank you.

On the VIN number, the lists here are from Yamaha USA and compiled by an expert on Yamaha models.  There are bikes out there from other countries and they don't always use the same series of VIN numbers as the USA. 

Pictures of both your frame and engine VIN would be helpful.

Front wheels were 1.40 vs 1.60 and rear wheels were 1.60 vs 1.85 between the Enduro and MX....  tires were also definitely different sizes and tread patterns between the models.

The close ratio gear box was offered as optional "MX conversion" parts and there was a CT1-C Enduro version with the close ratio gears from the factory.  (But not the AT1-C)

I do not know what is going on with the serial numbers, but I can swear in court that my machine has matching frame and engine numbers as stated and I have seen the listing online for a machine with a slightly higher number. I have searched the same charts you have and I cannot find a serial number listing beginning with a four anywhere, for any Yamaha model of that vintage.

The only reason I mentioned the tire sizes was that in your spec chart you show only the smaller sizes.

As I said, I did not mean to imply that you did not know about the close ratio gearbox. I mentioned it because the issue seems to be difficult to find.

Welcome from NZ. Gonna be fun to have you along. More the merrier i say. Enjoy your ride--on here.

Greetings from Tennessee 
 Pictures would be great you can use google photos, Imgur, dropbox etc 

To the person who wanted to see photos of my frame and serial numbers, your site states that photo uploading is unavailable. If this changes, I shall be glad to take a couple of shots and send them in.

Yep the 'pic thing' is out of action but can link to an external thingy like Imgur.
I use google photos--not sure why i chose 'that', but it works for me, or maybe it just links it but not a live photo.
If we have arguments on here they're mostly just "Robust Disgussions" lol.

I wasn't challenging you on your serial number... Yamaha documentation is not always the best. Evidence helps document the "undocumented" and maybe solve the mystery.

Years ago many people were adamant that every VIN that wasn't in the tables must have been something like a stolen bike that someone had re-stamped. Some obviously were not legitimate. Others definitely are.

Other country models still have a lot of mysteries... but some have been solved. Here in the US there are a lot of bikes from that era that may have been brought from overseas by someone in the Armed Services so that's always a possibility.

Yamaha specs in official documents themselves often contradict themselves or are just plain wrong... so it doesn't surprise me that you found something incorrect. The reason I mentioned the wheel differences is because it's obvious that an "MX" came with knobbies and they look larger... what's not so obvious is the actual wheel rims were wider as well.

No sure if i'm stiring the pot, but my 1970 AT1 frame number is AT1-417130. Engine number should be the same as motor has never been changed. Well, i have pics or video up here somewhere showing it as 'a now' 175 [top end]. But motor bottom end has never been out of the frame.
Directing this to OP post #1. I'm in NZ.

The engine # 418229 is stamped into the top of the engine case on the left side. The frame # 418229 is stamped or engraved directly into the frame on the steering head. There is no plate attached including a manufactured date, as I have observed on other motorcycles. I have never examined the steering head of another Yamaha Enduro or MX, so I do not know if the lack of a plate attached is the usual way it was done on these models.