a) Since the mechanic said he checked the petcock and it was ok, how does he know? Did he follow the suggestions of the forum here to test it or did it just "look" ok?  I wouldn't take his word for it unless he did the recommended petcock tests outlined by this forum.

b) Make sure you have no leaks in your carb vacuum line. A small crack will let air leak out thus decreasing your vacuum pressure and lessening the ability for a properly functioning petcock to deliver fuel.

c) make sure your gas cap is venting and not clogged. Doesn't really make sense that this would be your problem, but the more you ride and bounce around the more pressure in the tank can build up (or the more a vacuum can build) causing crazy things to happen with your fuel flow.

d) If it only seems to happen after the bike gets warm/hot, could be a spark plug getting hot and fouling out as one suggestion mentioned.  Test your plug or get a new one to eliminate that as a possibility.

e) If it only seems to happen after the bike gets warm/hot, are you sure that you don't have a loose header or muffler connection that is changing shape when it gets hot thus creating an air leak, which leads to loss of backpressure and possible rough running?  Don't go wrench the header bolts down and break them, they are only supposed to be snug, not superman tight!

Maybe none of this is your issue and maybe you have tested all of these things?  I dunno...

Good luck!  

I took suggestions from this site to him and he checked several things including the petcock.  When he came to pick it up after it stalled the last time he checked the gas line and it was getting gas.  Once it cools off it starts right away.    When it has happened if I sit for a while, like 20 minutes it will start up but  I don't always get stuck in a convenient spot with a wide shoulder so it was time to get it looked at.  I've heard good things about this guy from 2 different bikers and took him on their recommendation.  So we shall see.  The dealer in the area is thumbs down.

I agree with you but for me outside of the oil change I have no knowledge of the mechanics of a motorcycle.  I'm learning a little  as time goes on so maybe someday I will be able to do the work.

I think Justin has a good idea. Get a Raptor.
They are cheaper than a mechanic's flat rate.

Eventually you will change the petcock. So why nor now?

My practically brand new petcock is sitting in my garage. I changed it because I new it would eventually give trouble. :'(

I can do the maintenance on a lawn mower, push type, except for sharpening the blade, that is change oil spark plug and clean carb.

I freely admit I don't know much about engines.  But I had the petcock issue, and I don't recall any backfires because of it. It would silently die at highway and low speed and not restart until I turned it to Prime.  I put the Raptor on, it was easy and I was lucky it didn't leak.  I don't think the petcock is his described problem (but it will be a problem).

This backfire and stop, does sound electrical.  First it's running normally, fuel flow is normal, then spark is interrupted, engine still turning, fuel is still flowing unburnt thru the muffler, so it backfires.  Right?   So it sounds like a skinned wire close to a hot part.

Ero4444A skinned wire next to a hot part? A skinned wire would care less about the part being hot or not , a bare wire would jump to ground on a metal part no matter what the temp. If the bike has spark to start,the only way the spark would fail is if the ignitor  unit failed ,this could be seen buy clamping on an induction timing light.Logic-is the best tool in the box,the bike has compression,spark, fuel? I have advised him to buy and change to a raptor to no avail ! He has a "mechanic "that leaves the bike on the side stand idling ,to go work on other bikes,until it stalls (wonderful) this should give you some idea about what this guy knows or cares about fixing the bike! Stick a fork in me ,I'm done! SO BE IT!

Hello
I am the person who started this conversation.   Just to clear up a bit of the comments, nearly everything that was suggested he did and to no avail.  The only time the bike backfires and stops is when it has been ridden for a while, even up to 40 miles.  Once it cools down, maybe 20 minutes it will start again.  I don't see his idea of letting it idle as crazy as it did finally backfire and stop while in his shop.    I am an older female with little knowledge of motorcycles except for oil change and checking tire pressure.  I thank all of you for your suggestions and be glad you can work on your own bikes.