Hi all , I have a 2012 sinnis stealth 125 (winter hack,project bike,bit of fun) it didn't run when I 1st got it (bad starter relay) so replaced that it ran for a bit (badly) but now it just will not start at all , stripped the carbs a million times , checked the valve clearance at least 20 times an they are fine .....sometimes (completely random times) it'll start for a few seconds an die when the carb was on it would turn over an when I stopped it would make a hissing sound ....without the carb it makes a sound like a cork being pulled from a wine bottle right as it stops turning over ........any ideas? ...it has fuel,spark, compression so I'm stumped on this one literally any ideas welcomed and appreciated