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JON, Small Engine Technician
Category: Small Engine
Satisfied Customers: 1209
Experience:  Certified Small Engine Technician
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I have a &S 21 HP Platinum w/XRD and full pressure lub.

Customer Question

I have a B&S 21 HP Platinum w/XRD and full pressure lub. (whatever that means). this is a vertical shaft Craftsman YT3000 mower. It puffs dark smoke at starting (black carbon inside ext pipe probably from choking at start. After running awhile it smokes out the ext intermittently, mostly when hard turning the mower. I have to add some oil (5-6 oz.) every time I use it. engine runs fine. I cranked it, removed the dipstick and put my hand over the opening expecting a small amount of suction but there was none, probably very slight positive pressure was noticed. Any Idea what is causing the smoke and oil loss.
Crankcase is not overfilled. there are no oil leaks.
Submitted: 10 months ago.
Category: Small Engine
Expert:  JON replied 10 months ago.

Hi, my name is ***** ***** me review the issue, and I will be more than happy to help resolve it as quickly as possible.

Expert:  JON replied 10 months ago.

If you are not leaking oil, but are losing it, and smoking black smoke, the rings are allowing it by, and the rings will need to be replaced on the piston

Customer: replied 10 months ago.
black smoke is from not enough oxygen to fuel when the choke is engaged. spark plugs are not fowled or show signs of oil. engine runs great. occasionally puffs smoke while cutting only while turning. Why would you not think the crankcase breather is letting some oil get to the carburetor?
Expert:  JON replied 10 months ago.

it can be, but being as you never stated oil was in the carb, I would not assume that is was. If you have oil in the carb, then just as you have stated, the breather assembly is not functioning properly and allowing this. You are not going to lose 5-6 ounces of oil through the carb and it run just fine. That is a lot of oil to use at one time, and nothing be leaking. It sounds to me like you know what the issue is already, so I will OPT OUT so you are not charged or another expert may assist you.