Briggs & Stratton Blowing Smoke

[EddieC]

I put a new B&S engine (INTEK 17.5 HP - Model 31R907-0006-G1) on my Snapper riding mower 3 years ago. All running great until today when it started BLOWING SMOKE..... a lot of smoke. Pulled the oil dip stick and smelled of gas. Changed the oil and blew a small amount of smoke on first start. Second start had no smoke and runs smooth. Any advice on what's going on here. Here's a link to a You Tube 20 second video showing what's happening:

 

[TylerFrankel1]

I've seen this many times... I believe your issue is a failed needle/seat valve in the carburetor. This valve regulates gas flow into the float bowl. The needle tip is made of rubber and if it becomes at all distorted it will allow gas to flow into the carburetor and overflow it. The overflowing gas travels from the carburetor into the engine and cylinder head. It then slips past the piston rings and fills up the crankcase where the oil is with gas. That's why you smelled gas. This raises the level of oil way too high as it is diluted with gas to the point where basically a 50/50 oil gas mix is seeping into the combustion chamber and other places it doesn't belong when the engine is running. That immense amount of oil burning causes smoke. If you change the oil, voila, that gas is gone from the oil and it's back at the right level, so the smoke will stop. However, it will happen again if you don't address the carburetor. Either replace the needle/seat, replace the carburetor, or install an in-line fuel shut off valve that you shut off when you aren't using it. I'd start by using a shut-off valve and seeing if that solves the problem. Cheap, quick, easy and if that doesn't solve it no harm done. If it does work and if you're comfortable with it leave it that way. Otherwise, replace the carburetor or needle/seat.

This is probably happening because of the crappy ethanol gas we're forced to use nowadays combined with Briggs having awful QC as of late. And I imagine you may have let this thing sit with gas over the winter which can exacerbate those factors.

 

[EddieC]

I've seen this many times... I believe your issue is a failed needle/seat valve in the carburetor. This valve regulates gas flow into the float bowl. The needle tip is made of rubber and if it becomes at all distorted it will allow gas to flow into the carburetor and overflow it. The overflowing gas travels from the carburetor into the engine and cylinder head. It then slips past the piston rings and fills up the crankcase where the oil is with gas. That's why you smelled gas. This raises the level of oil way too high as it is diluted with gas to the point where basically a 50/50 oil gas mix is seeping into the combustion chamber and other places it doesn't belong when the engine is running. That immense amount of oil burning causes smoke. If you change the oil, voila, that gas is gone from the oil and it's back at the right level, so the smoke will stop. However, it will happen again if you don't address the carburetor. Either replace the needle/seat, replace the carburetor, or install an in-line fuel shut off valve that you shut off when you aren't using it. I'd start by using a shut-off valve and seeing if that solves the problem. Cheap, quick, easy and if that doesn't solve it no harm done. If it does work and if you're comfortable with it leave it that way. Otherwise, replace the carburetor or needle/seat.

This is probably happening because of the crappy ethanol gas we're forced to use nowadays combined with Briggs having awful QC as of late. And I imagine you may have let this thing sit with gas over the winter which can exacerbate those factors.

Great suggestions! Thank you. Lot better than replacing the engine again.

 

[TylerFrankel1]

Great suggestions! Thank you. Lot better than replacing the engine again.

Definitely a lot cheaper... 698183 is what you're looking for as far as shutoff valve. Local mower shop should have them.

 

[slomo]

Blown head gasket. Common thing on those Inteks. Or oil level way too high. That is definitely burning oil.

Not a carb issue at all. Not with all that smoke.

slomo

 

[StarTech]

I have seen engine with polluted oil (gas/oil mixed together) to smoke quite heavily. As OP mentions it was overfilled when checked and the oil change cure the smoking problem. Probably had run for nearly 10 minutes if the muffler got filled with oil.

Repairing the float valve leakage problem is best. Most likely the OP has the Nikki carburetor which need the float bowl gasket set as the o-ring on the transfer tube usually goes bad. Ethanol has little to do with it as o-ring ages and shrinks causing the leakage. I haven't seen much problems with the Ruixing carburetor but they are fairly new to the system.

Adding a remote fuel valve only masks the problem as the problem will get so bad that engine will start to flood while running.

Now the Briggs 310000 series does have it common problems too, One is the Nikki leakage due aging rubber, Second is they tend to blow head gaskets, and third is the ACR failure on the camshaft.

Blown head gaskets are easy to find if we all did a leak down test when adjusting the valves. Note when replacing a blown head gasket always check head warpage. I just did one that had over .005 warpage.

ACR failure usually causes hard starting problem. Just note that when the ACR turns loose it can take out the oil slinger/governor assy.

 

[TylerFrankel1]

Blown head gasket. Common thing on those Inteks. Or oil level way too high. That is definitely burning oil.

Not a carb issue at all. Not with all that smoke.

slomo

If he smells gas in his oil, then short of him putting it in there by mistake, how would it end up there? Just saying...
i only have a few years experience in the industry but I see a failed needle/seat Nikki carburetor making a lawn tractor smoke come through like twice a week where I work.
It’s possible he blew head gasket but changing oil would not make the smoking stop if that was the case.
Of course I have also seen a failed needle/seat cause a head gasket to blow, because the cylinder gets hydro locked with gas and then when it’s cranked over the excess pressure can blow it.

 

[TylerFrankel1]

I have seen engine with polluted oil (gas/oil mixed together) to smoke quite heavily. As OP mentions it was overfilled when checked and the oil change cure the smoking problem. Probably had run for nearly 10 minutes if the muffler got filled with oil.

Repairing the float valve leakage problem is best. Most likely the OP has the Nikki carburetor which need the float bowl gasket set as the o-ring on the transfer tube usually goes bad. Ethanol has little to do with it as o-ring ages and shrinks causing the leakage. I haven't seen much problems with the Ruixing carburetor but they are fairly new to the system.

Adding a remote fuel valve only masks the problem as the problem will get so bad that engine will start to flood while running.

Now the Briggs 310000 series does have it common problems too, One is the Nikki leakage due aging rubber, Second is they tend to blow head gaskets, and third is the ACR failure on the camshaft.

Blown head gaskets are easy to find if we all did a leak down test when adjusting the valves. Note when replacing a blown head gasket always check head warpage. I just did one that had over .005 warpage.

ACR failure usually causes hard starting problem. Just note that when the ACR turns loose it can take out the oil slinger/governor assy.

Yeah unfortunately these are pretty junky engines. Camshafts love to come apart and yes head gaskets like to blow too. The Nikki carbs are a PITA. Hard to work with and fail a lot. I try and find Walboro replacements when available, or I buy aftermarket eBay carbs. No sense in spending 120 bucks on OEM when they’re leaky low quality anyway. Ethanol is known to deteriorate rubber, and the Nikki carb has that giant o-ring thingy as well as a needle seat made of rubber. I have seen what ethanol can do so I avoid it personally, whether or not it’s the sole cause of carburetor failure. Could be entirely wrong but non ethanol gas is only a bit more expensive so no harm done.
But in OP case, the oil smelling like gas and being too full before changing, and the fact that changing it solved the problem (for now), that basically guarantees his problem is needle and seat.

 

[StarTech]

Yeah unfortunately these are pretty junky engines. Camshafts love to come apart and yes head gaskets like to blow too. The Nikki carbs are a PITA. Hard to work with and fail a lot. I try and find Walboro replacements when available, or I buy aftermarket eBay carbs. No sense in spending 120 bucks on OEM when they’re leaky low quality anyway. Ethanol is known to deteriorate rubber, and the Nikki carb has that giant o-ring thingy as well as a needle seat made of rubber. I have seen what ethanol can do so I avoid it personally, whether or not it’s the sole cause of carburetor failure. Could be entirely wrong but non ethanol gas is only a bit more expensive so no harm done.
But in OP case, the oil smelling like gas and being too full before changing, and the fact that changing it solved the problem (for now), that basically guarantees his problem is needle and seat.

Well the Nikki in my opinion a very simple to fix carburetor. And the OP engine they came with the NIkki or Ruixing depending on date code. On the particular Nikki that is shown in the IPL you can replace the needle and seat (fuel transfer tube) all day long but if you keep using the old gaskets it will continue to fail. This particular uses an op-ring on the transfer tube that tend to be the cause of fuel leakage. I rarely replace the needle on these Nikki carbs to fix a fuel leakage issue.

Also these do o-rings on the main jet that tends to get loose causing those inexpereince repair person to lose them easily.

As for Ethanol, carburetor cleaner is just as damaging to rubber parts. Personally I run 10% Ethanol in everything here without problems. My personal mower has been the same Nikki for over fice year since it last cleaning and was just fine last week when I took it apart for a checkup.

 

[Scrubcadet10]

If he smells gas in his oil, then short of him putting it in there by mistake, how would it end up there? Just saying...

generally if the needle fails while the tractor is sitting, fuel flows into the intake and combustion chamber and past the piston rings,

Now, i will say i repaired a Kohler CV15 a few weeks ago, gas dripping out of the muffler.... needle failed and drained the entire gas tank, and i don't know how, but i checked the oil, the oil level was perfect, not diluted and didn't smell of gas..
how it didn't get past the piston rings, i don't know. however i did change it out to err on the side of caution, and it needed it as it was pretty dark./old.