Hi there once again!
  Many thanks for the kind responses regarding any recommendations for a good tool to remove the armature from my 1971 Yamaha AT1-C 125 Enduro. 
  I’m awaiting the delivery of what I hope will help me to remove the armature and then replace the left side crankshaft seal. 
  What I really need to do is figure out why the bike needs to run with the choke on and when I take the choke off, the bike acts like it is starving for fuel and requires me to open the throttle quite a bit to get the bike to run halfway decent, but it wants to die out unless the throttle is nearly wide open.
  I have completely cleaned and rebuilt the carburetor with a proper NOS Yamaha carburetor kit and a new float needle and seat. I’m at wits end and would once again enlist the help of the many fine members here on this website.
  I would also like to contribute to the forum somehow as well. I have owned and ridden many of the Yamaha Enduros since I was a teenager and I still enjoy them greatly to this very day!
  I haven’t made any attempt to do so as yet, but, I have many, many spare parts in my personal inventory and I am going to be “thinning” the herd a bit, so to speak, in the near future.
  In any event, once again, if anyone can be of help and share their insight with me, I would be most appreciative of any advice and support.
  Many thanks in advance and I hope that I might be able to get involved and be of help to others as well.
  Take care and stay safe!

    Best regards,
                           Bob

Where did you find an actual Yamaha carb kit?  If Yamaha made them, I can't say I remember ever seeing one.

Generally clogged pilot jet is most common reason for that issue...  could be air leak too...  didn't you say you were removing armature to replace crank seal?  Use the 77-79 IT175 ignition side crank seal as it's a proper dual lip seal.  Might want to address that and any other air leaks before carb work?

I've also found there is a wide variation of what "rebuilt" or "restored" means...  and carbs are one of those things that people often have to clean more than once before it works correctly. 

   Hi there once again!I used Mikuni parts that I have had for several years now. I did not mean to intentionally mislead anyone. In any event, I will have a close look at the pilot jet and see what happens. On the other hand, I have just located a very fresh looking carburetor in my inventory and I will try to do a swap and see if that might make a difference.   To give a brief synopsis, I was riding the bike when it lost most of its power and was producing huge amounts of blue smoke in the exhaust.  I have had the same symptoms when a piston skirt fractured and went through the engine and spit out most of the fractured parts.Needless to say, it damaged the cylinder and head, but, after a complete tear down and subsequent machine work, the bike was soon up to speed again. In this case, the right crankshaft seal literally was blown completely free from the crankcase and the result was the loss of power and the engine getting oil transfer from the transmission into the lower end of the crankcase.  Once I replaced the right seal, the bike fired right up and idled normally, but, it doesn’t run normally unless under a full throttle application. I am planning on replacing the left side crankshaft seal as a precautionary measure and to minimize the the chance of the same thing happening again.  I work out of the country quite a bit and my time at home in the USA is very precious, so, I hope that I can get the bike into optimal running condition and enjoy it before I have to travel again in the near future.  Again, many thanks for any advice or assistance and if I can return the favor, please let me know and I’ll do my best!  Take care and stay safe!    Best regards,                            Bob

Dual air sources create a need for the choke to be on.

asco

 

Don't waste your time trying to dial in the carburetor until you know for a fact your engine is in good sound running condition. Crank seals good? Cylinder top end good? Timing set and ignition working properly? Then set your float level and make sure all your jets are correct sizes and the carburetor is spotless inside out. 

      Hi there!
  I have installed a fresh top end and new crankshaft seals. The timing is spot on and everything else looks good!
  I spent the entire morning rebuilding the carburetor yet once again, but, somebody suggested that the culprit might be the pilot jet. I swapped the carburetor for another known carburetor from my other AT1-B and the bike started and ran perfectly!
  I then reinstalled the original carburetor with yet another fresh rebuild, this time with a brand new pilot jet and the bike started right up and ran perfectly!
  Of course, I was so happy and I wanted to ride the bike to make sure all was indeed well, and wouldn’t you know it, it had a flat rear tire! I fixed that and the bike is now back up and running like a champ and I will take it out for some gentle riding and seat the new piston and rings. The bike is nearly 53 years old and the cylinder is still on its standard bore!
  I now will tend to my other two AT1-B’s and will replace the crankshaft seals and do a thorough cleaning and rebuild of the carburetors. I’ve had very good luck with these bikes over the last 53 years that I have been riding them and they are still amazing machines indeed!
  Please accept my deepest thanks and gratitude for your kind assistance and suggestions! They did not go unheeded and the results speak for themself!
  Please take care of yourself and enjoy the upcoming weekend! If I can ever be of help to you in any way, please drop me a note and I’ll do my very best.
  Once again many thanks!

      Best regards,
                               Bob

Congrats.