Idles, no Rev

Hello to all.
I have a 81 XS, that I put points in 6 or 7 years ago. Few years ago I put in a Pamco.
It also has a magneto and capacitor. Problem I have is bike starts 1 or 2 kicks and will idle itself out of gas, but dies when you rev it.
I bought it to my friend how helped build it, he came up with the capacitor being bad.
Put a new one on from TC Brothers and bike ran like new again.
He put about 40 miles on it no problems, I took it home and also put another 40 miles on it with no issues.
Yesterday I took it for a 10 mile loop and by the time I got on my road it started to sputter and backfire and limped the last half mile home.
Now right back at ground zero of idle all day but won't run.
Any thoughts.
Thanks in advance
Russell

I might try a battery instead of the cap. Most any battery will work for testing.
You won't have to get fancy for the test. even carrying the battery in your pocket with the wires running out to bike will work for testing.
Leo

My buddy said thing time for a good old battery.
Went with capacitor for easeabilty got 6 or so years no issues now this.
Gonna give battery a shot.
I'm not worried about fancy lol

If it runs fine with the battery I might suggest a closer look at the charging system. Perhaps a weak ground somewhere.
Leo

I was thinking of regoing over the wires, there's not a whole lot of em.
Was thinking case pulled cap and put new on on made it work and figure maybe just moved something just enough

Ok so I throw the volt meter on it, capacitor without motor on is holding 5.75, start bike it's got 12.75, hit the throttle and it drops to 5.
Missed wire, bad capacitor haven't tried battery yet

UPDATE!
Put on a battery and she runs like a top and charges at 14.8.
Guess its till to build a battery box

Happy days are here again !!!!!

Scott