I have two 68 DT1's One has a screw in idle adjustment.at the carburetor. The other has a throttle cable adjustment.. . Which one is correct for the 68? Thanks Stan

Probably depends on VIN as to where in the production year yours was made. As you know many changes by Yamaha that first year. Both of mine are top adjust. Both bikes under VIN 13000. Maybe Enduronut knows? I haven't seen that break point printed anywhere in those old manuals or knowledgeable collectors. I'll be watching what others think. 

The supplement at the back of the 71 DT1E Service Manual in the Tech Library shows many of the changes made to early DT1. 

It says that change happened with the DT1B model but as we all know sometimes changes came out earlier.  The bulletins in back of that manual do show serial numbers for mid 68 changes like the frame and fuel tank.  I don't think it has a serial number for the carb change. 

But if you search the site our resident 68 DT1 expert Enduronut has posted details of which carb stamping belongs by VIN:  Here's what he says:

Carb flange stamping
1. E1 = 1968 to serial # DT1-002850
2. E2 = (Domestic) was only used in Japan
3. E3 = 1968 # DT1-002851 through 1969 # DT1-015829
4. E4 = 1969 # DT1-015830 through 1971

Thanks Mark T for posting. Pretty sure it wasn’t in the back of the 71 manual and I have referenced that back section several times. I’m excited to compare the carb stampings to my bikes. Hadn’t seen a reference to that before.

I have a Australian DT1 parts manual which shows the changeover occurring
at engine #15830 , which would likely be at the start or close to the start of 69 model year .
 

That coincides with Enduronut's info...  I was guessing the E3 revision still had the idle rod and what your parts manual says seems to confirm that? 

The '68 I am tediously procrastinating in refinishing had a side idle adjust carb, but it also had a later year pipe. Well striped down for a pit bike as well (so....many missing bits). I was able to obtain a top idle carb with an E3 stamping, although by the list here it is not quite correct for my VIN (1717). Oh well. 

Press on and keep looking I suppose. One of these days I hope to start posting up some pics of what has been done. Certainly not going to outdo any I see "in process" so far! 

Cheers!

 Well I’m bummed…I checked both my 68 DT1 bikes and my stamps are weird. Hopefully Enduronut or MarkT or any other person with more experience than me can shed some light. Both my carbs are top idle adjustment. Both my carbs are stamped “214” with “M1” beside or beneath. On the opposite side of the flange it has a star. Both stamps are on top of the intake flange. Both carbs are the same. I took some 4/0 steel wool and gently went around the flanges so I am sure to see any marks. I’ve posted pics of both carbs showing the 214 M1. One pic shows the star which is the same on both. Any ideas?

I could be wrong but fairly sure the "M1" might mean you have MX (or GYT) carbs?

Well Mark T that is interesting. Both bikes have the single vertical spark plug which I understand are 68 GYT heads. I didn't even know there were GYT carbs. I wonder what makes a carb a GYT part? I haven't worked on either motor yet so haven't cracked open anything motor wise. Very interesting and I hope more info comes in. I'll look in some manuals that list GYT parts for conversion and see what I see there. Really intrigued now.

Edit..The rear of the carb for the air cleaner boot doesn't look any bigger than my other early bikes...I'll take a measurement.

Second edit...in my 68 Rider's Manual it lists racing parts available from Yamaha but doesn't refer to them as GYT specifically. It lists a racing carb part number 214-14101-70 and has VM30SH in the notes. I can't see a tie to my carbs yet though. I'm not sure how to measure to check for the "30" . 
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