Small Engines (Lawn Mowers, etc.): Briggs Motor lots of smoke, head gasket, cold engine

Question
Hi Ben,

Hoping you can help with this one... I have a 28N707 14.5HP B&S. for the past year had small amount of white/blue smoke appear when starting but then would disappear after about 10 seconds of the engine running. Last week, after about 10 minutes of use, the unit started blowing heavy white/blue smoke, and eventually the motor died. Tried to restart, couldn’t until an hour passed, then restarted with heavy smoke. I then started my simple diagnostic step (the only one I know, and requires no tools) take off the air filter and look at the carb. Examining, I noticed oil in the carb intake orifice. I thenI did some reading on this and many suggested that when this happens to replace the head gasket, which I did, but still heavy white smoke after starting. I then read to change the breather, did that too, but still heavy white smoke but no oil back in the carb. I then noticed that my oil was very diluted with gas. I changed the oil and then after starting, no smoke initially, but after about 2-3 min, white smoke again (not super heavy this time). I checked the oil again, and couldn’t really tell if there was gas mixed in.

I’m stuck whether I should consider rebuilding carb or if a complete engine tear-down is needed.

Thank you for any thoughts you can provide…

Paul

Answer
Pau

Sounds like you will need to either replace your carburetor or rebuild it. What is happening is the Float needle is letting gas leak into the ignition chamber and then since it is running or not running it gets by the rings and into the oil causing oil & Gas to be mixed in the oil pan.


Oil burning gives off blue smoke, but the engine may be running so rich it is diluting the oil with gas. That would make the oil thinner, and it could slip past rings into the cylinder easier to get burned away. You can check this easily with a cold engine. Pull the dipstick/plug, get some oil on your fingers and smell them. If you smell gas, you've got your answer. Won't work as well on a warm engine, cuz the gas vaporizes and is driven off. Fix the air filter/carb.