my friend asked me why his tiller is smoking bad, but starts okay ,the only things I could think about was a bad ring,i a I also think those engines mix the fuel and oil and fire in the combustion chamber,is there something wrong with that oil pump?..muffler looks good and spark arrestor is gone.
The GX25 is a 4-stroke motor, and uses regular unleaded gasoline (not 2-stroke pre-mix). There's a dipstick and filler hole for 10W-30 oil just other 4-stroke motors.
Bad smoking (white smoke?) likely indicates failed piston rings and/or damaged cylinder walls, allowing oil to get pulled into the combustion chamber, and volia!, white smoke. From the examples I've seen, this can typically happen if dirt/debris is allowed to enter the engine, usually due to a poorly maintained and/or damaged (or missing!) air cleaner filter.
A tiller is used in a dusty/dirty environment, so it's critical the air filter is working and fitted properly. I'd take a look at it first, and see if you see any traces of dirt inside the air cleaner toward the carburetor. This would confirm dirt has been ingested into the engine, and (probably) what led to ring wear/failure...:frown:
Now if the smoke is black/dark, it could just be the engine is running rich (too much fuel) so the choke could be stuck or other issues with the carburetor...