have a friend rev it up when its cold and put ur hand infront of the exhaust and if it spits shit out then smell it......if it smells like gas its probably gas, u could also try to light it when it shoots out......if its gas, it will burn LOL good luck, sounds like ur runnin rich or the timeings a little off on the exhaust cam, it happend to my old prelude......have fun.......

miles