Gonna re-open this post because maybe something posted earlier is relevant?

Anyway towards the end of the season last year I was on the highway going about 60 and I noticed my rpms started dropping. So naturally I opened the throttle more but felt no response (if anything my rpms started dropping more!).
Bike ended up dying and I pulled over to the side of the highway, tried starting it up but couldn't get her going. Got picked up, let it sit for a day, came back, started up, rode off the highway and it did the same thing (rpm drop -> engine stops -> can't start). I eventually got it home through repeatedly getting it started riding a few miles (maybe 5 minutes) and letting it sit again for > 1 hour.

It's sat for a good 6 months now and it's finally nice enough to ride again, but now I can get it to start but it backfires a ton and it still dies after about 5 minutes.

From the very little I know/have gathered it seems I have a rich fuel mixture causing the backfiring but I'm not sure if I just should clean the carbs again? The spark plugs might be fouled by now, I've also heard it could be the fuel petcock?

tl;dr lots of backfiring, bike starts but dies after ~5 minutes

Anyway just looking for some advice and/or a point in the right direction. Thanks!

 

I had exactly the same issue, turned out when I took the tank off and put it on the ground, the bleed tube got blocked. That caused a vacuum to form in the tank as fuel was used up. Eventually, the pressure was low enough to prevent fuel flow into the carbs. As soon as I opened the filler, the vacuum was equalised and the bike stared! I took the tank off, unblocked the breather pipe, no problems since.