sparks/smoke

i was just thinking back to last summer when i got my girlfriends bike running. my friend who helped me out with it hopped on it and i got on his bike and we went for a little ride. we got on the express way and he had it pinned in top gear for quite some time, i guess looking for a top speed (its a honda cl350)and suddenly sparks started flying out of what looked to be one of the pipes. i thought at first it might have been something else like the chain rubbing something, i didnt know at the time. then smoke started pouring out of one of the pipes. we got off at the next exit and he said he lost a cylinder. he didnt know about the sparks and smoke at this point. it started running fine on the way to the gas station down the street and hasnt given us a problem since. any guesses as to what may have happened there?

i had a simmlar problem with my z1 900.i was riding down the street and allof a sudden it bogged down and white smoke poured out of the pipes she revved up and has ran great ever since. i found out on mine, the problem was the rubber hose from the crankcase to the airbox got gummed up. so i cleaned it out and i have had no problems since. i dunno about a honda 350, but it should be a similar setup. i hope this helps