Vuka rm 125 starts, idles fine - when start riding, it feels like it runs out of petrol and cuts out.

not it is not normal and indicates a very serious problem for such a young bike. If it has a carby then the float is not sealing of properly and the fuel is flowing into the cylinder ,past the rings and filling up the sump. May be some one left the fuel tap on the last time but it is something you need to have fixed before you hand over any hard earned cash

it could be that your carb dont open fully

Those little carbs on these tiny thumpers clog easily. You'll probably have to pull the carb, soak it in carb cleaner, blow it out with compressed air (be sure to wear chem-proof gloves and a face shield or at least eye protection--carb cleaner's nasty and when you blow it with compressed air, it goes everywhere). Reassemble, and it should run fine. We had a TTR125 and we had to clean the carb this way every year before riding season.

vuka rm125 has no timming chain it is a pushrod engin you should adjust the vaves cold at0.10mm

you need ajust the floats in the bole to let more fuel in

Your black ignition box may have gone bad. Or your stator plate came loose and changed your timing.

have you tried turning the tick over screw in ?
carb may need cleaning ie idle jet which is the very small one located next to the main jet
try these first if no joy you may need to look at the piston and rings condition because low compression could also cause this problem
hope this helps

the idle buddy is too low,on the carb is a screw the ide screw turn it in 1/4 of a turn with the bike running untill it idles the way you want it too and it will idle the pic below ill help ya buddy

But it runs fine other wise? as long as you keep it above idle runs fine but then dies at idle? id so then you need to clean the carbs the slow jet is dirty. hope this helps

sounds like the float in the carb might be sticking stopping any more fuel getting through to the engine