139QMB random idle issues

[moru]

Hello everyone! This is my first post to ScootDawg, glad to meet you!

I am posting because I have a strange problem with my scooter.
I have a Peda Shotgun 50cc, with 139QMB engine and I have some problems with the idle .
The scooter starts ok from cold, running great for about 15 minutes of riding than it looses the idle. After another 5 minutes of riding the idle is again stable.
I don't know what to think. Everything else is ok. Even when I loose the idle the engine goes ok, no bogging on load or any other things, except that he can't stay at idle speed.
I have seen that when looses the idle, the engine runs lean (if I cover the air intake, the engine will idle).
I have tryed another carb and the problem persist.

Any ideeas that might help ?

Thank you!

Later edit:

I think I have found the problem. When I switched the main jet, I've put grease on the carburettor's gasket to fix it on position. It seems that the grease wasn't a good ideea because it got into the pilot jet.

I have cleaned the carb and everything is ok now.

Thank's