check engine while running, help Options

[empite]

Hello guys , I have a half cut st205 that when I start the engine the check turns off and after couple seconds turns on again , 3 things cause this probably and I want to make sure who exactly knows very good the motor .
1)I use a fuel pump that is probably from lower cc engine because the fuel recycling that does (when the pump send the fuel to the fuel filter and after to the engine becks and after all the fuel is more than it needs goes back to the reservoir) is very low I can record it with video if you don't understand what I mean. So does the engine check cause by fuel low compression?
2) does the engine check appears cause some fuel becks needs to be clean? Or the check engine doesn't appear if the fuel becks doesn't work or something like that?
3) theres a valve for idling rpm i think, that's missing

The motor on idling runs with 700 rpm and sounds like needs more fuel or some fuel beck doesn't work...
What do you think guys ?

Thank you in advance

[Smaay]

the stock fuel pump will be fine. you really need the codes to diagnose what the problem is. Low fuel pressure will not cause a CEL