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AC710

Briggs blowing smoke

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AC710

Mr Steele's carburetor question reminded me of a 70's vintage Toro snowblower I had with an 8 HP Briggs engine. This engine would start on the first or second pull in any weather, but when started cold would blow an enormous cloud of gray smoke for a few seconds before clearing up and running like a champ. I had to replace the carb because corrosion had pitted the bowl and mixture tube so it would not seat. Also, it was warped so it would not seal to the manifold. The new carb took care of the loping/racing problem but did not change the smoking problem.

So, what was the smoking issue?

The choke was set properly and caused no issues once it was opened. There was no linkage so I had to reach down across the engine and under the  snow cover to close/open the choke. I drilled a hole in the cover and attached a simple wire control that made it much easier to use. Regardless, the smoke was not choke-related - not black and not affected by choke operation.

The engine used a little oil, but nothing out of line for a 30-year-old engine.

The smoke was a dense gray, choking cloud that literally filled up the area under the deck where I stored the machine. People even called thinking the house was on fire! Once it cleared, the engine did not smoke noticeably, had plenty of power and ran great.

My theory is that the valve guides were worn and oil pumped up past them while the engine ran, then seeped down on the piston and sat there until the next start-up. Once the oil burned off - making the cloud - then things ran normally.

Any thoughts from you folks that are more versed in B&S than I am?

I did not pursue the problem because I found a screamin' deal at Lowe's on a new Troy-built blower at an end-of-season sale and retired the Toro. Sold it at an auction in the spring. Bad idea, the new one has been nothing but a PITA with numerous issues going on and on. The old Toro had another problem that influenced the decision to trade up. The wheel-drive shaft was worn so it would not hold the roll pin for the chain drive gear. It was shearing off grade 8 bolts a couple times a season. I got so I could drop the bottom pan and replace the "pin" in about 15 minutes - but of course it always broke in the middle of a plowing project.

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MrSteele
8 minutes ago, AC710 said:

My theory is that the valve guides were worn and oil pumped up past them while the engine ran, then seeped down on the piston and sat there until the next start-up. Once the oil burned off - making the cloud - then things ran normally.

You hit it on the head. OR

If the engine was tilted in the frame of the blower, did you add oil to the top of the filler hole on the top side? I had a tiller come to me that smoked awful on start up. The engine was 'tilted back' on the frame when not in use. When the tines started digging, the base of the engine leveled out, and the smoking stopped. Aggravated the owner til he brought it to me. I scratched my head on that one, too. One day, I started the tiller, it smoked, then I tried it in my garden. Smoke went away. I checked the oil while in the garden and it ran out of the filler when I removed the plug. Hmmm The sump was overfilled badly. Solution? Check the oil with the tiller engine sitting level, no more smoke on startup

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AC710
1 hour ago, MrSteele said:

If the engine was tilted in the frame of the blower, did you add oil to the top of the filler hole on the top side?

Nope, not tilted. The amount of oil in the crankcase had no effect on the smoking. Just-filled or needing a pint or two - no difference, and the smoking only (and always) occurred when cold-started, never when running. Such heavy smoke you couldn't see through it, with an acrid, rather than over-rich-flooding smell - very distinctive. The engine started and ran well right away, no rough running or starving. There was no primer and little choke needed to start. 

I did experience the effect you suggest after tilting the machine up to change the drive pin, but that is to be expected when laying it on its head and cleared up very soon.

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