HI and thank you for your question.
This could be a couple of things here, and with a little methodical diagnosis, we should be able to sort it out fairly quickly.
One thing you mentioned was fuel in the float bowl. That is an excellent start but may not tell the whole story. If the float level were off, too low, it could have fuel, but starve for fuel on top end when consumption is at its highest. After the engine quits, and you come to a stop, it could be starting to fill back up and give the illusion of sufficient fuel but maybe isn't. We can check that with a running fuel level check or you can pull the carb and measure the float height.
However, before I advise you to check that out, I would really like you to do a compression test on the engine and see how that looks. An internal combustion engine requires 3 elements to run. Compression, fuel and spark. By doing the compression test, we are ensuring that we are not running into some sort of a mechanical issue and causing it to quit.
Another suggestion would be, carry an extra spark plug, and when the bike quits, stop as quickly as possible and put the new spark plug in the cap, ground it and spin the engine over and see if it is still sparking. We need to figure out which of the 3 required elements we are losing and causing it to die.
If our compression is solid and we are not losing spark, then we have a fuel problem. It could be something going on with the main jet in the carb too. Since you see fuel in the float bowl, it is unlikely it is a venting issue, but we need to keep that in the back of our mind as well.
Check those things out and let me know what you come up with. We can take if from there if you need more help.