Hey guys, I have a stumper here. My dad has a Craftsman riding mower (I think that is the problem...haha, I worked for Sears Service Center for a couple of years so I can say that) that has started having problems. First, it is about 3-4 years old but I don't know the numbers off it. It is a single cylinder B&S, 18.5 HP I think, maybe 18HP. He called me a while ago and said that it has been running funny, so I went out this weekend to look at it. The stupid thing will start and run at low to mid-speed. however, as soon as you try to get it up to full power it starts sputtering and I noticed some blow back through the carb vent tube (the plastic one coming out from under the engine cover/cowl). He has replaced the carb already and that didn't help. I rebuilt and put the old one back on, still no help. He also replaced the coil/plug wire because the old one melted a bit by the muffler. One of the first things I noticed is that the fuel filter doesn't fill with gas. It will run, but there is just a bit of gas at the bottom and looks like the filter is acting as a wick to pull the fuel up. I think that is an issue. I replaced the filter, no help. I think the pump might be bad to start with. The thing I am most afraid of is that the OHV's might be out. When I was at Sears and the other shop, OHV was just starting to be big in riders, so I didn't get to work on them much. Could this be a case of a valve not seating back properly? Wouldn't that happen at all speeds instead of just the top end? If you think it might be the valves, how can I check/adjust/replace one? I have done a lot of old valve jobs, and I have worked on OHV's in cars a little bit.
I am stumped and hope someone can recognize the symptoms or tell me something else to look for.