HI all,
I joined the community a few years back when I rebuilt a 1970 HT1. That bike has been great fun and I still ride it. I have acquired a 1971 RT1MX according to the vin. Was just a frame and engine when I salvaged it. I have since been putting it together piece by piece. I actually got it running a couple weeks ago and have had it on a couple test rides, but now it has lost all spark and it seems like the ignition coil quit. I'd like to get a NEW coil for it instead of a used one off of ebay. DOes anyone know if this is possible? Or, perhaps I can interchange it with a DT250 coil as there seem to be plenty of those on ebay. The RT1 coils seem to be few and far between. Thank for your help!

You might check with member DEET, he might have a new original one if you're determined to fire off the parts cannon.  (Not very common for ignition coil to go bad.)

P.S.  Some of the new aftermarket ignition coils on ebay are total crap. 

Coils are pretty reliable & usualy give some indication if packing up rather than just quiting.
If you still have your HT1 i'd try the coil off that if its a runner. Or try a coil off any other magneto ignition yamaha you might have.
Check points for obvious gap & give them a scratch.
Be sure it not just a shorted out spark plug, or even plug cap.
I guess you're way past that& i'm just woffling on,--but i hate spending money until i'm sure other mag things are ok.
Well--i just hate spending money full stop haha.
Welcome back. Miss my HT1, was a fun bike.

Thanks guys. I fiddled more with the magneto and re-soldered the wires onto the condensor and was able to get spark again. Now I've got to get the carb tuned.