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Oil use in lawn mower

My somewhat old lawn mower has begun fouling its plug. I think it is oil, not sure. Briggs calls for 30w or 10w30.

  1. Will 10w30 burn significantly faster than 30w?
  2. the plug is j19lm. I might be able to go to a hotter plug as a temporary fix to burn off the oil.
    What would be the next hotter plug?

That’s the hottest I’ve seen. Maybe running too rich? Black puff from muffler on start-up?

I have one old mower that burned a lot of oil. I switched it to 10W-30 full synthetic and it cut the oil.consumption by more.than half. I bought the 10W-30 full synthetic for $2.79 a quart under the RK brand name at my local Rural King store.
In the at big box stores you will.find spark plugs that.replace the J-19 that are.meant.for mowers that use oil.


No, there’s usually a blue puff. Maybe me priming it too much.
Then it runs with no smoke.

Can you post a photo of the plug?
Black & dry is generally too much fuel. Black & wet is generally oil.

You could always try a J11C, a bit hotter plug, to see if it stays cleaner. I attached a link to a chart (the best I was able to find). There’s a risk you’ll end up screaming “holy piston!” but on a lawnmower the monetary risk is small.

Briggs changed their oil recommendations to allow or encourage 5W30 synthetic year around. I have switched all my engines to synthetic now. I don’t know if it would help or hurt but I’d try it anyway. Good point though it might be fuel and need a carb adjustment or cleaning or parts.

You might want to try an RJ 19 LM spark plug. The R designates a resistor plug which may provide a hotter spark. The LM means it was designed for a lawnmower.

So, if it was running too rich wouldn’t it smoke?

Install an anti-fouler in it .

It can run pretty rich and still not show much black smoke. On the other hand it is pretty hard to get them not to run rich and still have good power and acceleration. For oil use, I did try installing chrome rings for that purpose once but ended up just junking the engine and putting a new one on.

My single cylinder Briggs lawn tractor was fouling its plug. Most of the time it would puff black smoke on startup. Turned out to be the carb inlet needle valve was slightly leaking and produced a small pool of gas inside the carb throat between uses. The carb never dripped gas on the outside.

So, this mower is about 10 years old. I am not much of a mechanic except on old cars so I have no clue how to adjust the carb. What I am getting to is that I think it may be rich, as the deposits are not oily. Maybe I should throw it out. I bet a repair shop would charge $75 to do that.

Have you cleaned or replaced the air filter? If the air filter is plugged up it will “choke” the engine/carburetor.


I think @Nevada_545 may be onto something. At the beginning of each mowing season I replace the air filter on one of my mowers that has a paper filter and on my other mower that has a foam filter, I wash it in a dishwashing detergent, squeeze out the soapy mixture, let it sit for a few minutes, pour a little motor oil into the foam, squeeze out the excess oil and it’s good to go. I picked up a used mower for $15 that ran poorly, so I added carburetor cleaner to the gasoline-- I think it was GumOut. It did the trick for that mower.
We have had a very mild winter here in east central Indiana. I haven’t had to use my snow blower once. Our grass is beginning to green up and the crocuses are blooming, so in three weeks or so, I am going to have to get our mowers going. We had such a late fall that about all I could do when I put the mowers away for the year was to fill the gas tanks and add a fuel stabilizer.

Air filter changed often.

As well as mixing some GumOut in the gasoline, you might try removing the air cleaner, start the engine, and spray carburetor cleaner right into the carburetor. Let it sit for a minute and then start the engine.
I don’t know what a replacement carburetor costs for your engine. I had to have a new carburetor on my 2 stroke tiller and I bought one online for $25.
One final thought:. You are using fresh gasoline aren’t you?

I solved my rich-running by buying a fuel shut-off valved at Tractor Supply. After each mowing, I first close this valve and wait for the engine to start missing before shutting off. Next mowing, turn on valve and start. Haven’t fouled a plug since.

Edit: This assumes you have a regular carburetor and not a gas tank/carburetor combination typical on a 3.5 hp Briggs.