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I have to rebuild the top end of my hisun 450. Can I replace it with a 500 cylinder kit without any other modifications?

I have a 2018 model Hisun 450 EFI UTV. I have done over 6000 trouble free kilometers. About 4 weeks ago i felt that utv was not performing like it should. Done a compression test and found to be low. Replaced rings as they were worn. I drive in a very dusty environment. The problem of low power is still there. I have checked cam timing, valve clearances, compression up to 9.5 bar, done leak down test and valves are seating, stripped and cleaned fuel pump, removed and cleaned throttle body, checked for leaks on throttle body manifold, replaced spark plug, tested stator coil, tested hv coil, checked all electrical connections, checked injector. UTV starts easily and idles for 5 seconds and cuts out. When utv starts, it will rev up the first time and then start to miss as if it goes into a limp mode. If i lift my foot of the accelerator utv will idle for 2 seconds and then die. It starts immediately again. Would the air flow/ air pressure sensor or exhaust gas(lambda) sensor cause this. I cannot test them as dont know the correct values. Any suggestions will be highly appreciated.