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stewrun · Apr 7, 2007, 03:01 PM

Help
My Briggs-powered lawn tractor is in a sad way :( . I can start it and it runs fine for 3-5 minutes. Then as I'm mowing, it will suddenly belch a massive cloud of smoke and stop running. It doesn't seem to be throwing any smoke out the exhaust before this happens.
I've ready around the Net a bit on this, and I've heard it could be a bad breather, a blown head gasket, etc. Anyone know if I can diagnose better what the exact problem is before I order a bunch of parts? Thanks!

Brian (stewrun)

newaukumdon · Apr 7, 2007, 11:41 PM

Drain the oil and refill to the proper level ensuring that there is no fuel mixed with oil. If there is fuel mixed with the oil the carburetor is leaking and will need to be rebuilt.

The crankcase operates under vacum so when the breather valve is faulty, the dip stick doesn't seal or it has a blown headgasket the crankcase loses its vacum and oil is pushed out the breather vent into the aircleaner. This is far more rare than the overfill of oil or fuel mix problem.

Let us know what works.

Don

stewrun · Apr 8, 2007, 08:45 AM

Originally Posted by newaukumdon

Drain the oil and refill to the proper level ensuring that there is no fuel mixed with oil. If there is fuel mixed with the oil the carburetor is leaking and will need to be rebuilt.

The crankcase operates under vacum so when the breather valve is faulty, the dip stick doesn't seal or it has a blown headgasket the crankcase loses its vacum and oil is pushed out the breather vent into the aircleaner. This is far more rare than the overfill of oil or fuel mix problem.

Let us know what works.

Don

Thanks Don
I drained the oil and man there was a ton of fuel in the pan! So, it looks like I have a bad carb? I took the valve cover off and fuel poured out of there also! Is there any way to adjust the carb to cut back on fuel flow, or must I rebuild/replace it?
Could the overfill of oil/fuel in the pan have caused the smoke cloud/stall behavior? Did I mess up the breather and head gasket because of this too?
I know, lots of questions - thanks so much for your help!

Brian(stewrun)

newaukumdon · Apr 8, 2007, 11:22 AM

Common problem often misdiagnosed, the carb has a needle valve that sits in a seat. When the float chamber is empty the float hangs down and allows fuel to enter the chamber, as the level in the chamber rises the needle seats and stops the flow. The needle will not seat because of either debris or just a bad seat.. . You can flush the fuel tank and the crankcase and try again paying attention to the oil.

YES, the fuel will cause the smoke and NO it probably did no damage.

Good luck,
Don

bpsew · Sep 5, 2009, 07:58 AM

Check your head gasket. Mine did the same thing. Started smoking all off a sudden. This is a common problem for this engine. The head gasket will blow will by the overhead valve chamber. Then you have pressure in the crank case. The pressure will push oil into the breather.

Thanks
bpsew

ebilly · Mar 21, 2012, 04:14 PM

The carb problem is the most likely one in this case. Mine was letting gas flow into the intake all the time. Of course, it will go into the little tube that goes to the PCV box on the side of the crankcase, and then into the oil. It will also go into the cylinder if the intake valve isn't fully seated, and often will seep in there anyway. It will wind up in the overhead valve chamber if the engine is turned over or run. The vacuum in the crankcase will suck more fuel into the oil after the engine is run and not turning over. One big mess either way and lots of smoke. The carb has to be rebuilt or replaced. Depending upon the carb LMT number, the kit may or may not have the nozzle that goes up into the center of the carb, over the after-fire solenoid. If either seat, on the inlet, or this nozzle doesn't seal, the carb can leak gas.

This comment is for anyone who searches and finds this. Hope all helps.