Instructables

My mower smoked and won't run?

I was mowing with my push mower (brigs and Stratton) and suddenly it blew out a large amount of white smoke and stuttered to a stop.  Later that day I tried starting it again and it almost started up but it sputtered and filled the area with a plume of white smoke.  Now (a year later) I decided to attempt to get it running again.  I am not sure about taking out the spark plug because I think it may need a torc wrench or something.  I did however check to see if it would still spark one of my spare plugs which it does.  The fuel in it is still the same so I may try draining it and re-filling it.  It smells like gas.  I have heard of water and oil being probable causes, could this be true.  I know that it has mistakenly been filled with the mix of oil/fuel from my chainsaw's can.  I drained it, but could there still be oil in it or something.  Can I pull my spark-plug out with a mere crescent wrench and replace it?

Vyger3 years ago
From your description it sounds like the head gasket might have blown. It is replaceable but it takes work and tools.
Most people at this point would just junk it and get a new one. If I were you I would look at it as a good learning opportunity and try and fix it. After all, it can't get any worse, --------- unless you light it on fire.
It could also be a broken valve, but if it was that you would not get any compression, so the fact that it almost started suggests its the gasket.
jj.inc (author)  Vyger3 years ago
THANKS, I pulled the spark plug, It was either soaked in oil or gas and when I looked around it was oil so I guess you are right it is the head gasket, lucky me I just got a whole metric and inch socket set.
Vyger jj.inc3 years ago
If there is a lot of oil in the combustion chamber then the problem could be the piston rings. Small engines usually only have one and if it broke then its letting everything just blow out through the crankcase. Either way your going to have to tear it down. Rings are not hard to replace and not very expensive either. Its just time consuming to disassemble and put it all back together. A trick I learned is to take pictures of everything as you take it apart and you make yourself a guide for reassembly. I would also look for a engine book on the engine (not the mower) so you can get all the specs for putting the bolts in and to the right torque.
jj.inc (author)  Vyger3 years ago
Well that was a year ago that it almost started, I have already replaced it and am just doing this as a learning experience, glad I am not the only person around who still does that, I added some gas and still nothing so I think I am gonna do this, thanks for your help. :)
seandogue3 years ago
White engine exhaust usually indicates the presence of water in the combustion chamber. Blue smoke usually indicates the presence of oil.

Since your push mower is probably not a water cooled engine, where a blown head gasket might allow passage of coolant from the block into the intake manifold or directly to the combustion chambers, I'd suspect it got water in the gas tank.

I'd start by draining the gas tank, removing the spark plug, blowing the combustion chamber out with pressurized air, allow to "air dry for a day or two, and then clean the spark plug, regap, re-install, and refill the gas tank with fresh gas. 
jj.inc (author)  seandogue2 years ago
That sounds like a good plan, but I don't think it is right. The mower isn't going to smoke a huge amount and then stop in a time frame of about one second just because of the presence of water.
It will if there's enough water present.

But I see you've identified the problem so my info was moot.
Gas goes "off" and leaves deposits in the carb and things - strip the carb and dunk it in cleaner for a day or so, flush the tank with some more carb cleaner and refill with new gas. MOST mowers are 4 strokes, so DON'T use 2 stroke mix !

Getting the plug OUT is pretty easy, but you must be very careful to not over tighten it putting it back or you will strip it.

Steve
jj.inc (author)  steveastrouk3 years ago
Thanks, would you happen to know if it strips the plug or the engine. And do you need to replace an oily plug.
In general, the rules of life say it will strip the most expensive bit - ie the head :-(
I agree with Ork, there's a lot in the idea of finger tight+ 1/4.

Steve
Depends on the metals, but stripping the engine is certainly a possibility in cars, especially with today's lightweight-metal engines.

If you don't have a torque wrench, there's probably some rule of thumb like "as tight as you can get it with your fingers, plus a quarter turn"... but I haven't played with small engines anywhere near enough, so you should get someone else's advice on that.