Since your carb has been recently rebuilt it wouldn't hurt to pull it quickly and check for dirt. You sound convinced it's an issue with voltage, I know it may sound dumb but I had a positive battery cable that if you moved the deflection as little as a half an inch voltage would drop significantly, would work for a while and then act like yours is. I found it only after having replaced the same components you did, wrote it off to needing to be done anyway, and I kept the coil as a spare. :thumbsup:
Intermittent grounds can cause a lot of grief as well, I got into the habit of going around my 135 twice a year, spring and fall, to clean all the terminals connections, saves me the grief of having to do it in the middle of a snow storm.