Bike runs well, however...

1.) electric start only clicks and barely turns the governor  
     I pulled the stator and checked the brushes they seem ok, maybe I need to pull the armature?

2.) during a ride if I turn the headlight on - bike runs poorly, then blows the main fuse housed at rear fender area

I've scowered this site and read the manual believing I could figure this out to no avail - any thoughts?

Thanks in advance for any direction

Not accidentally connected the battery back to front. Can get away with it on a generator system but not alternator type. Ok not that. Are all brushes contacting the commutator & connected properly. Sorry i'm no help. They gave no trouble back then when i worked for the local shop. Do they have a charging light on the tacho & if so i guess its not going out so not charging. Does the generator look good--not like someone's had a play & damaged things. Hope more help arrives soon. Cheers from NZ. ps, i had one of those for a while--trade in at work--& a good little bike it was too.

Firstly i know nothing about the 12V system on the AT 1.
However, from what you've described, you are losing energy from the system and therefore the coil hence the poor running.
Do what you've stated already and get the multi meter out.
If you have a good manual, follow some of the suggestions for testing components on the system.
Then measure back on the wiring to the lighting side including the ignition switch. KISS applies when looking for faults like this ,and yes i have been there even recently. Check and clean all the contacts . I would like to bet you have a leakage ( high resistance) around the handle bar headlamp area.
Start by removing the switches and making your own earth to a clean point, like the engine mounting bolts, see if you get the same problem.
I hope that's some help.
Regards 
Shyted

 

"KISS applies when looking for faults"

One of the few acronyms that I like - Keep It Simple Stupid! 

I'm stupid & i over-complicate things lol so that theory doesn't work--for me anyway.

How many amps is your fuse and what wattage is your headlight?

It sounds like something in the headlight circuit is shorted or simply too much load.  You might also have the wrong fuse. 

I probably asked, but is it charging at all. If it keeps running until you turn the headlight on it sounds like it might be just holding its own but no more. generators really 'get into it' like an electric brake if its tout close to 14.5-15 volts. You could be right & might be a short in the field windings--wildly guessing.

The 12 volts 125 models need both a good solid, well-charged battery to run and e-start. The brushes, even though they look good, are likely worn down quite a bit. Some of the brushes included a wear mark about halfway down, not sure if all do. Right now Yamaha doesn't have them available but they were insanely expensive when they had them. The only reliable supplier is OldPartsShop on Ebay who is located in Singapore. link to his store is: www.ebay.com/str/oldpartsshop?_trkparms=...542580.m47492.l74602

He doesn't always have them listed, but you might inquire if he has some if not.

Thanks Mako.

I believe that Yambits here in the UK now supply repro brushes.

I really appreciate every response - I'm going to begin with the KISS advice first and work my way out from there.  

I'm enjoying the challenge - more to come and thanks again!