I am going to assume you have the LMH carb on it. It has the large 4 bolt flange for the air cleaner. It came 2 ways. One with a fixed jet bowl nut and one with an adjustable main jet bowl nut. If adjustable run engine at high idle and turn needle in till engine starts to stumble lean then turn out till stumbles rich then set needle half way between the 2 settings. If engine doesn't accelerate smoothly from low idle to high idle turn screw out about 1/4 turn more. If you blow oil out the breather hose check the drain holes in the breather are not clogged. If i get time i will get some pics of the breather of my OH140. Does it have the fuel pump that screws into the carb body?
My carb says Walbro on it and it has the adjustable main jet bowl nut and yes the fuel pump was screwed into the carb. It wasn't working right and I'd had it apart a couple time so I just took it off and let gravity pump the gas . When the fuel level gets down a ways and I'm going up a hill sometime it runs out of gas. Then I blow in the gas tank and fill the bowl and get off the hill. I didn't see any drain holes in the breather. I started it up a couple days ago and it ran OK and wasn't blowing out any oil. I moved the log splitter to the porch on the garage and after unhooking the splitter I noticed it was puking oil out the breather tube again. I had that happen with a flat head Briggs once. I made a gasket for the breather and those little holes were covered by the gasket and it puked oil. After some trial and error I cut out where the holes were and the puking stopped. I have a new gasket on the OH160 breather now and it is different than the one that was on it and I think that old gasket was one I made years ago after replacing the head gasket. I had bought some OH160 parts off ebay a while back and a gasket kit was with the parts and it was for more than one size engine and the breather gasket was thicker, about 1/8 inch, and covered a smaller area.
That engine on that Struck Big Job looks like mine. I assume it has the rectangular valve cover with 2 screws holding the breather and valve cover to the head. Where are those drain hole in that breather? I took pictures but I can't figure out how to reduce the size of the pictures to meet the attachment requirements.