Problem: The ATV starts and runs at idle perfectly. But as soon as I open the throttle, the engine starts to slow down until it stops. On the attached video you can hear the sound of how it works: see video below
Prehistory: there is a Polaris Sportsman 500 1998, which for about 1.5 years stood in repair, including also replacing CDI with one taken from the same ATV. Finally, the vehicles were on wheels, traveled several kilometers and overheated - forgot to fill the antifreeze Came back home in small moves. The next trip started well, but after 10 km there was a feeling of a small drop in power (even as the vehicle got warm completely) but still drives. Next trip - the situation is repeated. The next test of ATV through time and a huge loss of power from the very beginning. The engine sneezes, does not want to go more than 5 mph.
What has been done: the carburetor has been replaced with a new one (inexpensive, $ 40), a new spark plug, a new ignition coil, the engine head has been removed, the piston is in good condition, valves were corrected - but the problem was definitely not in them.
Ignition control unit is suspected. Who faced similar? Please help in solving the problem.
Thanks in advance.