I recently purchased a used Craftsman YS4500 riding mower with a B&H 21 hp single cylinder Intek engine. I purchased the riding mower from a neighbor who indicated that the mower ran fine last year, but when they began using the mower this spring, it emitted a large about a white & blue smoke and that oil was spraying out the muffler. I assumed that the problem was a blown head gasket. Even though I have little experience with small engine repair, I did dissemble the mote and found that the I the head gasket had indeed failed. I replaced the headgasket and also thoroughly cleaned the carburator and installed new seals & gaskets. I also replaced the air and fuel filters. After completing all of those items, the mower started right up. However, it was running very rough and appeared to be backfiring through both the carburator and the exhaust. Once the mower warms up a bit it runs fine, until I increase the throttle. If I increase the throttle quickly, it will start to miss and backfire. However, if I increase the throttle slowly, it will run smoothly. Once I engage the mower blades, it immediately backfires and runs rough. However, if I decrease the throttle, the engine will begin running smoothly. I can then slowly increase the throttle and it will run smoothly and I can mow the lawn. However, at times, without warning, the engine begins to backfire again. When this happens, I stop the mower, lower the throttle until the engine runs smoothly, and then increase the throttle slowly.
I understand that something is wrong with the engine and I cannot continue to operate it with this problem. I suspect two things... from what I have read, it seems that the issue is either a timing problem that could be caused by a sneered, or partially sheered, flywheel pin. Or, it could also be a valve problem in which one of both of the valves are not always seating properly. However, when I replaced the head gasket, I throughly cleaned the head and the cover including the valve seats. I also used Seafoam gas additive to clear out any remaining carbon deposits on the valve seats. The mower actually seemed to ran a little better after the Seafoam treatment, but it still backfires when I engage the mower deck.
I am looking for guidance on where I should look next. Or are there other possible causes that I should investigate, before I pull the head off again to inspect the valves or before I pull the flywheel to inspect and replace the pin. I will appreciate any advice from those of you that are likely far more experienced with small engine repair than am I.
I understand that something is wrong with the engine and I cannot continue to operate it with this problem. I suspect two things... from what I have read, it seems that the issue is either a timing problem that could be caused by a sneered, or partially sheered, flywheel pin. Or, it could also be a valve problem in which one of both of the valves are not always seating properly. However, when I replaced the head gasket, I throughly cleaned the head and the cover including the valve seats. I also used Seafoam gas additive to clear out any remaining carbon deposits on the valve seats. The mower actually seemed to ran a little better after the Seafoam treatment, but it still backfires when I engage the mower deck.
I am looking for guidance on where I should look next. Or are there other possible causes that I should investigate, before I pull the head off again to inspect the valves or before I pull the flywheel to inspect and replace the pin. I will appreciate any advice from those of you that are likely far more experienced with small engine repair than am I.
