Maintenance

First of all your engine does not have a carburetor. If it is back firing through the intake the ignition timing is probably way off.

Ok now where fo all thd plugs attach on the wiring harness

I think you have your sparkplug wires all mixed up and it's firing at the wrong cylinder. If you had your wires off, try finding where they go by checking length and rub marks. There's only four cylinders so it shouldn't be too hard. But if you didn't have them off, leave them where they are.