Subject: backfiring ambo...

after a long ride today, started backfiring out of the exhaust - while
sitting at idle...also, it's not wanting to idle..i reset idle screws to
1.5 turns out (after continually turning them up to get it to idle...so
i could get home..) i'm assuming points/plugs are the culprit. once out
of idle it runs fine...any other ideas?