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750 Kaw. Vulcan...difficult to keep idling after bike warmed up..cuts out and won't hold idle..some gas smell, some back firing what's up with that?
did tune/up ie..fluid change, air filter,sprk plugs etc...just got from dealer and they're "procreating" around so i want to inform myslf about the prob.

Can you tell us more? Had the bike been sitting? Have you played with the carb adjustments at all? Tried to adjust the idle yourself? Hard to know without more info, but my initial impression is that it sounds like dirty carbs - specifically the idle jets might be partially plugged. I am not an expert by any means but I've had similar experiences. I'd try adjusting to a higher idle speed first - but if that doesn't work and the bike runs strong when you give it throttle I'd say it's your idle jets and you might need a good carb cleaning. Your mileage may vary!

i don't know if this bike has been sitting? the bike starts well when cold with the choke...but once its been running for 30- 40 mins..and once i've shut if off and let it sit for an hour or so it starts up well but it won't hold an idle when i'm sitting at a traffic light ..it back fires a little when gearing down..when i'm reving the throttle to keep it running it sometimes sputters almost like fuel is having trouble getting through..and after its been running a while the gas smell starts....kms are 10000kms ..actually i tipped it on its side and after doing that these problems really started so maybe i flooded the carbs shook up debrisetc.. but if this is part of the probs..wouldn't the fuel drain from the carbs and the bike run properly again?

Check out this post, he to smells gas.
http://totalmotorcycle.com/BBS/viewtopic.php?t=2408

I'm not sure bfunkay. I don't know that bike. But it does sound like a carburetion issue in general. I'd certainly play with the idle adjustment and the screws that affect the mix on the individual carburetors before ripping them apart, but if you can't get the mix right with little adjustments I'd say you are going to have to dip the carbs. Please don't act on my advice alone though - there are better mechanics here than I, hopefully they will weigh in. I've had this problem myself and was able to correct it as described but please get a second opinion. In general, bikes that have sat for a long time without having the carbs drained almost always need a full cleaning, but we don't know that for sure about your bike.

Does that engine have hyraulic valve adjusters? If not, it may need valve adjustment. Valves partially open can cause all of those symptoms, especially if it runs okay until it's warm. As the valves wear at the seat, the clearance between the valve and the cam decreases until it rides the cam all the way around and doesn't close fully. Open valves cause bad burning of the fuel (smell) and backfiring as the leftover mixture ignites at wrong times. Check the valves. If they're hydraulic, It could be timing.