Have 15 yr. old Murray lawn tractor with B&S 14 hp Vangaurd single cylinder 4 stroke engine. Over the past few months I find the following:

- Engine starts OK
- Begin mowing
- Within 10 minutes the engine sounds bogged and white smoke billows
- Take the load of engine by pushing in cluth and disengaging blades, the white smoke stops almost completely
- Let engine run a few minutes, white smoke stops, continue mowing
- After this I can usually mow without white smoke, but periodically the situation repeats if I hit some deep grass, in other words a very heavy load on the engine.

One other oddity - when I throttle down the engine often keeps running at speed, not responding to the throttle. If I momentarily place a load, say by engaging blades, the engine speed drops.

The engine uses some oil but not a great amount. I can't figure where to look for the problem. Perhaps something is worn or stuck in the carb and/or throttle linkage and/or choke?
Any advice appreciated.

 

Check the oil. Is it overfull? Does it smell like gas?

 

The oil level is within the correct range, actually on the low side. The oil does seem to have a gasoline smell to it, it's difficult to tell for sure. I don't know what that indicates but doesn't sound good. Thanks for replying.

 

If any gasoline is present in the oil, it is bad for your engine and also will increase the oil level, making it go in places it shouldn't. If there is gas in the oil, it is normally caused by a bad float, stuck or dirty needle valve. But if the oil level is not higher than normal, it shouldn't cause the engine to smoke excessively. Check your choke linkage, make sure it's all hooked up right.

 

If the oil seems thin and smells like gas, you have a leaking carb. Usually needle replacement fixes these carbs. Then drain and refill oil with SAE30.

Gas thinned oil can damage the engine, and cause it to smoke, even when the oil level gets low.