I have had three of these SX25 chainsaws over the years. These appear to be clones of the Chinese Zenoah G2500, a single hand aborist’s saw of 25cc.
Air leaks into either fuel induction, whether in the liquid fuel lines, carburettor gaskets, intake manifold or crankcase spells early death for two stroke engines. It quickly results in lean mixture, lack of lubrication, overheating and seizure.
The first two of these that I owned developed leaks in the fuel lines in the first year of ownership, Chinese plastic and rubber parts are not very reliable.
To head off problems, I have performed a simple pressure test now that the saw has about 10h use, it is about 1 year old.
The tank and cap are cleaned and the suction hose is gently fished out of the tank with a bent piece of wire. The filter is removed and in this case the felt unclipped to check the internal screen. The intake system is then pressurised to 50kPa, there should be very little drop over 5min. This checks the integrity of the hose from filter to carburettor inlet, the carburettor gaskets and diaphragms / valves in the pump and metering chambers and needle / seat seal.
This one is not quite perfect, but it is ok… to be checked again from time to time. (Turns out that testing at the nipple on the carburettor is near perfect, so the leakage is in 200mm of Chinese rubber fuel line.) This one has a purge bulb which provides another monitor point, any hesitation to quickly get pressure is a hint of possible leaking fuel lines (or could be an expired purge pump bulb or check valves).