Engine Smoking on Startup

MolaKule · Jun 4, 2004

FWIW

B&S 5.5 Hp push mower, manual start, manual push. Simple as can be.

My wife usually uses the push mower for trimming around her flower beds.

Every time she started it up it smoked for about 10 seconds. It's only about 14 years old.

OK, it has had Everything from M1 10W30, to Redline 10W30, to Amsoil ATM 10W30, and lately Schaeffer's #700.

I took off the head and found no worn rings, no scored cylinder walls, no bad valve stems, nuttin'. Replaced new gaskets all around.

Check carb; no leaking, no rich fuel mixture.

When I started it up from cold, there was never any smoking.

I found out she was pumping the primer pump about 4-5 times, whereas I only gave it two pumps.

Apparently, the 4-5 pumps of fuel was washing down the cylinder walls on startup and mixing the oil film with the fuel in the cylinder and fuel wash down, whereas two pumps just gave it enough for starting.

Her startup procedure has now been modified.

garyb80 · Jun 4, 2004

It's a good thing you caught that before the cops got you. You have to be at least 18 years old to smoke.

rg144 · Jun 4, 2004

How can you determine the condition of the rings from just pulling off the head? Or are you just going by "good" compression?

I have a 3 year-old mower that blows out grey smoke on startup, and just a hint of burning oil smell while running. (No wonder it was marked way down at Lowes). My guess is the gap in the rings are all in alignment instead of offset. But to check means taking it all apart. (A rainy day project).

My first guess was the dipstick was innaccurate but I changed the oil this season and filled with 12 oz as was printed on the mower deck and that put it a wee bit over the full mark on the dipstick.

Drew99GT · Jun 4, 2004

Redline in a push mower?

Hehe, as much as I have bashed M1 in the past, I must admit, I changed our good ol Toro mower over to it about 5 or 6 years ago and have not changed it since. The thing doesn't burn a drop or puff blue smoke ever and usually starts on the first or second pull after a long winters rest

JohnBrowning · Jun 4, 2004

It is funy Molakule because as I read your post I had my mind made up that it was a fuel induction issue. I was guessing carb until you ruled that out.When I was a kid I used to prime the heck out of the lawn mower until Dad caught me doing that and set me right! Dad was qurious why I got such a huge amount of smoke when I mowed the lawn. The lawn mower never did that when he mowed. SO he made me show him how I started the lawn mower. Now days always give them one prime and pull. If it does not start I prime it with another pump and pull. I have never had to prime it more then twice.

MolaKule · Jun 4, 2004

quote:

How can you determine the condition of the rings from just pulling off the head? Or are you just going by "good" compression?

Right. In the case of rings, I was going by good compression.

Borescope from inside crankcase (with piston all the way back on BDC) seemed to show rings were flexing, so I assumed no sticking rings. (Vee dooon't need no stickin' rings).

I thought I too had overfilled it with oil until I checked it again.

BTW, Anyone know of a way to inject mosquito oil into exhaust stream?

[ June 04, 2004, 11:22 PM: Message edited by: MolaKule ]

Bill Kapaun · Jun 5, 2004

Not a Briggs, but-
I trick I learned over at Garden Web regarding the Honda GXV 140 engines and the puff of startup smoke was -

Immediately after mowing, loosen the oil filler to allow the crankcase to vent. Apparently pressure/vacuum(?) doesn't allow the oil to drain down completely to the sump. Apparently this allows it to "puddle?" long enough in the upper engine parts to get into the combustion chamber causing smoke on the next start up.
It seems to work on my 16 year old Masters.

olddognewtrks · Jun 6, 2004

Unlike auto/truck engines, most lawn & garden engines are horizontal. On shut-off, the residual oil runs to the 'bottom' (actually the side of the cylinder and piston) and weeps past the rings into the combustion chamber. Thus the smoking on startup

. I don't worry about it, only if it keeps smoking while running. Just make sure there are no tree hugging fanatics in sight when you fire it up.

[ June 07, 2004, 02:10 AM: Message edited by: olddognewtrks ]

rg144 · Jul 4, 2004

I pulled my smoker B/S mower apart and found... rings perfectly installed. The problem? The crankcase vent! The contraption had locked up open. Occam's razor - look for the simpler solution. I'm now waiting for a new crankcase gasket to put the engine back together.

rg144 · Aug 5, 2004

Strange - I reassembled the mower, but instead of 20 oz of oil, used only 16. The result is no smoke on startup or while running. Dipstick showed between high and low; whereas 20 oz put it over the high mark previously. The label on the deck clearly says 20 oz oil SAE 30 for the engine. Seems strange if Yard Machine would get the spec wrong for the Briggs & Stratton engine. I didn't have to play with the crankcase vent as I previously concluded was the problem.

Matt_S · Aug 5, 2004

You know, my 5.5 HP B&S is the same way. 20 oz. puts it well over the full mark. I suppose I'll have to drop it down to 16 oz. from now on. At least I'll get two fillups on a quart that way.

tmorris1 · Aug 5, 2004

Where is the crankcase vent on these engines? I have a 4hp briggs that has started running a little rough and is smoking all the time. It happened all of the sudden. Could this be the vent?

rg144 · Aug 6, 2004

Opposite side of the engine from the carb - rectangular contraption with 2 small bolts holding it in place. Pull it off, the hole has a cover plate held in place by a spring. I guess it's like a pcv valve, if everything is moving around an loose (not gummed up), then it's doing it's job.

tmorris1 · Aug 8, 2004

I found the vent, it was hidden behind the muffler. Thanks for the info. Everything looked good, but I think a plugged air filter was casuing my problems. I cleaned and re-oiled the filter gave it the old Seafoam tune-up (neighbors love the white smoke) and now it runs great again. Would the plugged air filter cause the diaphram carb to suck air and oil through the crankcase breather since the filter was plugged?

rg144 · Aug 8, 2004

Hmmm, sounds plausible. I did a have clogged air filter prevent the mower from starting after winter storage one time. I had never had that happen before. Of course your air/fuel mix would be all wacked out and the governor wide open to maintain idle. (My engine is a 4HP B&S on a Yard Machine (MTD).

tmorris1 · Aug 9, 2004

quote:

Originally posted by rg144:
...... (My engine is a 4HP B&S on a Yard Machine (MTD).

That is the same engine that I have. I'm not sure how I like the diaphram carb though, you don't get very much speed control.

DockHoliday · Aug 9, 2004

My 6 HP B&S (~4 years old) was smoking after each cold start (after sitting a week). The engine had Mobil 1 10W30, so I added 1 OZ of LC (huge dose for this little motor), used it a few times, drained, put in some left over Mercruiser 25W40 dino, and no more smoke!

Grease is the word · Aug 9, 2004

Dock, that is hilarious -- I am using up my Merc 25W40 in my B&S lawn mower as well. It is a little tough to start, but it seems to like it.

DockHoliday · Aug 9, 2004

LOL - At 1/2 qt per year, I think I am good for the rest of the decade.

MolaKule · Aug 12, 2004

quote:

It's a good thing you caught that before the cops got you. You have to be at least 18 years old to smoke.

I was more woried about the tree huggers protesting on my front lawn!

Engine Smoking on Startup

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