50cc slowly dies when full throttle, HELP!

[islandRider]

[FIXED] - I had to buy a feeler gauge and adjust the valves

hi everyone!

I have a Wangye 49cc 193qmb 4-stroke scooter.
It has 8000+ km, but has given me almost no problems (besides a broken driving belt once ). That is until now...

Since 2 weeks ago or so it has not been able to reach its top speed (now 45-50, used to be 60km/h on flat road) and goes uphill very slow (35-40km/h, instead of 50 normal).

Then 1 week ago it started to act even more weird. Every time I start it up and drive away it will slowly lose power after 1 minute or so.
Even when I give full power it keeps going slower until I stand still and it dies on its own (Heres a video of it:
)
Then when I start it up again it takes a while. even when I give it some extra gas. So that makes me think it does not get enough fuel OR too much air, right?

Or could this be the carb? I could get a new one. But since I live in the Caribbean it will take some time and extra money to get it here.
I cleaned it with carb spray and cleaned the nozzles with pressurized air. But that did not fix it.
I checked for leaks in fuel and air lines and cleaned the fuel filter. Again, with no luck.
I adjusted the A/F screw and the idle. No luck either.
The only thing I could see what would be wrong is the spark plug OR the valves.

Oh and also, when i disconnect the fuel line the fuel flows out. So that's not the problem either :/

I hope I have given you enough information with this and the video. If not let me know and I will reply asap!