No FI light?
Your title says gas spitting out the exhaust, yet you only mention a charging problem?
I agree with 954Kevin on diagnosing, that is if you can keep the bike running long enough to do the test.
It needs to be at operating temp to get accurate results. But you can get an adea of how close you are even on a semi-warm engine. (I'm told by a tech-I don't know that for a fact.)
I guess the first thing I'd test is DCV coming to the battery right after you start it. Just hook a multimeter to each of the battery terminals. Look for at least 13 volts at idle and about 14.5 at 4000-5000 rpm.More than 15.5 is dangerous and means a problem. Stop the bike if it goes that high so you don't fry your battery or the rest of the electrical system. Flick the highbeam on when revving and see if that drags the voltage down and by how much, it should be minimal.
If your charging system is not giving you the readings you need, it's time to also test the stator before just slapping in a new reg/rec.
If your battery is any less than 12 volts at rest with engine stopped, (after a couple hour cool down from any charging), then it's toast. Need to replace.
Follow the wiring from the battery to the reg/rec, and inspect the condition of them. look for chaffing, or burn/heat signs especially at the connectors. Also find the three Yellow wires that run from the reg/rec to the stator and inspect them as well. Pull apart, clean, a dab of dielectric grease, and reconnect.
More to come when you give us some feedback.