Export thread

Hi. I have a craftsman mower with a 21 HP 540 cc Briggs OHV engine. It's about 8/9 years old.

It's been doing this random thing lately (only twice to me actually) once last summer and once yesterday.

I'll be riding and it doesn't start to sputter or anything, but a huge stream of clean looking bright white smoke (with a few short bursts of black) will just bellow out of the exaust for about 2 seconds smoking out the yard and then it just keeps on running, like I said no sputter or weird sounds, it's almost like someone threw a smoke grenade into the muffler as if the smoke has nothing to do with the operation of the engine. But it does come out of the muffler so something has to have gone "wrong" for it to do that.

Any ideas?

Classic oil in/on muffler.
First thing to check is leaks from the head or rocker dribbling down onto the muffler ( always do the easy bits first )
Next is oil leaking into the exhaust pipe.
Usually this is caused by oil pooling in th head around the exhaust valve guide till eventually it dribbles down the guide and into the exhaust stream to burn off in the muffler.
A little oil can make an awfull lot of smoke.
A crack in the head & leaking head gasket can also do the same but then tend to do it constantly.
Gasket will be all the time and a crack will start after 10- to 20 minutes running.

Last candidate is oil in the air box via breather caused by too much oil in crankcase, worn rings or leaking head gasket.
However the latter generally causes the engine to bog a little while it is blowing the smoke.

Finally there is oil sucked down the inlet valve guide.
I left this till last because usually it will be consistent varying from light grey puffs to James Bond smoke screens and also cause missing bad acceleration and hard startings as the plug will be carbon fouled.

Hello.

Thank you for the response. Sorry for the late response on my end.

I did some investigation with my mower and found that it was overfilled by nearly 20oz. (I drained the excess by trial and error into a drink bottle and checking the dipstick after each drain). Kind of funny, considering when we changed the oil and filter I made sure it was bone dry before putting in the 48oz it says right on the side sticker inside the hood. I put in exactly 1 and a half us quarts (48 oz) from the bottles when it was totally bone dry and yet it was overfilled by nearly 0.6 U.S. Quarts. that is probably a really good start. Next issue is the air filter.... It is oily and the stem where it attaches has an oily residue all inside of it. I'm going to have to replace that as well as the spark plug since, why not? It's original and probably getting ready to go, maybe getting fouled up a bit after this fiasco.

ALL your symptoms point to a leaking carb float needle valve contaminating your oil with gasoline. Running the engine like that may destroy your engine. I would immediately change the oil then ad an inline gas shut off valve and use it when the engine is not running. You can replace the float needle assý but chances are it will continue leaking anyway, an in line shut off is good insurance.

Walt Conner

If you still have the oil you removed smell it ans run it betwen your fingers, if it feels thin or smells of gas do as Walt advised .
And I will go one further as when I find fuel contamination I refill with supermarket oil run the motor for 1/2 hour dump the oil & refill again.
I repeat this proceedure till the new oil has amost no trace of old oil in it then do a final replacement with top quality red lawnmower oil.
For home owner you caould change the oil after each mow for the next 2 or 3 mows because Waly is correct it will destroy the engine.
Oil is cheap nd my view is always "when in doubt toss it out".

If there is no evidence of fuel contamination then just clean every thing up.
pull off the carb and the air filter housing and wash them both out, toss the old filters and see how you go again.
Because vertical engines have the crank case laid on its side they are highly sensative to overfilling which is why the warning about overfilling is actually on every dip stick.

No way the oil can be over full to the extent he says after he just very carefully filled it to prescribed level without the oil being contaminated.

Walt Conner

IF he was filling accordig to te bip stick readings I agree but the OP specifically mentioned that he added a specific amount of oil and made no mention of checking on the dip stick.
Have done similar more than once, wacking in the "right" amount of oil, sure I had drained the engine only to find when I went to do the final adjustment it is way over full.
Done a double fill more than once as well.

"I had drained the engine only to find when I went to do the final adjustment it is way over full."

Probably caused from being "down under" Don't have that trouble here.

Way over when filing to mfg, spec, come on.

Walt Conner

Sometimes you have to take the owners manual oil capacity with a grain of salt. Have a 35 hp vanguard on stump grinder that calls for 78-80 ounces of oil according to the OM. Shows full at 64 ounces.

Sometimes you have to take the dipstick with two grains of salt, may be the wrong dipstick for the engine. In 70 years of working on small engines, I have never experienced the extremes either of you have espoused.

Walt Conner

OP here.

Everything should be good now, thanks for the replies.

After having drained that oil, there is zero evidence of contamination with gasoline. Even checking the dipstick, that oil is perfect. The gas shut off valve idea is a good one, I'll look into it and if it's an easy install which I reckon it is, I'll do it myself.

As far as the wrong dipstick suggestion , I highly doubt this. The engine is pretty "new school" (from 2006) compared to a lot of older mowers I've used. It has a specific locking mechanism at the top that ensures it's pretty much only for that engine. No redneck replacement would fit, it has to be a Briggs one for that model engine. And when it was new the oil always read exactly full from factory oil. Never had issues. Not proud to admit the oil was changed for the first time in 2014, but this mower never had the smokey issue until after I changed it and apparently overfilled it.

Runs fine again after draining the excess...

Walt, I did the initial 5 hour oil change on that engine in my prior post when it was new. Drained about 64 ounces of oil out. So if it is the wrong dipstick, it would be incorrect from the factory, Discussed the 64 versus the 80 ounces difference with my Briggs distributor techs. And basically confirmed the difference in oil can be chalked up to the oil not draining from certain parts of the engine, like the oil cooler.

Correction to my previous post.

There may be gas in the crank case. The initial excess I drained out is pretty darn black, but I didn't suspect any gas in the oil then. I haven't actually needed to cut the grass since I drained the excess so all I did was run it for 15 seconds or so after I drained the excess.

What makes me suspicious is the oil right on the dipstick. As soon as I take the stick out, the oil runs off and drips ALL over the place like water. Yet, it doesn't smell like gas, it smells the same way when I used to do the oil changes on my old car - like old used oil. But it is only year old oil. Why is it so watery?

Please tell me it only happened because I had a lot in.... and if I do another oil change and be super careful about filling it Ill be fine?

I don't even want to dig in and fix the carb if that is the problem but I have no choice. Does anyone know what I need to look for, what I need to do? I don't know anything about carbs, let alone I am no mechanic, I'm just really technical and hands on but lack vital experience past changing the spark plug, air filter and oil on this mower. Chances are if I do the research online though I would probably be 100% fine.

Well I told you what to do then got scoffed at. Put in a darned inline gas shutoff valve and use it. I can send you a Service Manual for your engine IF you like. Address below, put in proper format and remind me what you want, engine model number.

Oil only a year old? Is this a serious post or a troll?

Walt Conner
wconner5 at frontier dot com

Check the watery thin oil on the dipstick for gas with a Bic.

Then fix the carburetor and add a fuel shut off valve and use it every time as a long term shut down procedure.

Tinkerer200 said:

Well I told you what to do then got scoffed at. Put in a darned inline gas shutoff valve and use it. I can send you a Service Manual for your engine IF you like. Address below, put in proper format and remind me what you want, engine model number.

Oil only a year old? Is this a serious post or a troll?

Walt Conner
wconner5 at frontier dot com

Click to expand...

I appreciate the kind offer however I believe I have the manuals still in our tool box. Plus I found a few pretty good resources online.

Also, what constitutes as a troll post. I'm sorry but I didn't come here to troll people who know more about my problem than i do.