I'm back, with a new XF...the old I've selled.

Is a XF650Y of 2000,that was stopped in garage for 3 years.
At first start, I cannot start, without deblocking the carburator filling level-stat.
With 2 new NGK10 with four contact.
The motor starts with long Stroke use, and POPPYiNG and BANGING at the exauhst system.
Running at 5000-6000 RPM there are two hole in power, and the feeling is always that there is to much gasoline in the motor or is missing some burns. In release of the gas, the exhuast explode like a FAST AND FOURIUS Byke!!
I putted in the tank some CLEANER for Carburator and valves with no particular effect.

Do you think tha depends on carburator? I'ts possible to put it in order without desassemblying?
Can I do some other check? Is there a particular connection for the spark plug (high RPM and low RPM)?
Vielen Danke fuer die Antowrten!
Ciao