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Briggs & Stratton 35 Classic engine, blue smoke + oil residue out of exhaust + Petrol in oil

#1

L

LochlanR

Just bought and serviced a 35 Classic engine on a push mower, Started it and there was alot of blue smoke, although I did have to replace two back wheels so I had it on its side for about 20 mins. When i got it the oil looked to be over filled quite a bit so made sure to change it to the right amount before starting it. After starting, it took ages to burn off the oil until it eventually cleared. Used it to cut the grass and left it for a couple days. Just went to start it now and it shot out a cloud of blue smoke, its been kept upright and not on its side, checked the oil, its gone very dark gray after one use and smells a bit like petrol has mades its way into it.

What could be the issue? I assume it to be the piston rings or something relating to that.


#2

R

Rivets

No, I’ll put money that the float needle is not sealing properly allowing petrol to run straight through the carb into the crankcase. Pull the dipstick and check if it is over full and smells like petrol. If it is time to replace the float needle and seat, plus change the oil.


#3

L

LochlanR

The carb looks like this, how would i go about changing the float needle?1691187438767.png


#4

R

Rivets

Sorry, I guessed on the wrong carb, me bad. Two things now come to mind. One, is it possibly that you put 2-cycle petrol in the tank? Two, could you have over filled the oil?


#5

L

LochlanR

Filled the oil to correct level, petrol is just normal E5 99 Octane from the pumps which ive used in all my B&G mowers


#6

B

Born2Mow

This is a common issue when any fuel tank is mounted above the carburetor.

Gravity can/will force fuel to flow into the engine. (This may assisted by a tiny piece of trash stuck in the carb's float valve.) From there the fuel bypasses the piston rings and dilutes the engine oil in the sump. Such fuel systems are often fitted with manual or "automatic" fuel shut off valve. The problem is that when the automatic versions fail (go Open all the time), there is no way for the owner to tell... except that the dip stick will show an excess of fluid in the engine's sump.

► The carb's float bowl valve is not infallible. Even with the best of carbs, it is never a perfect seal.

► Running the engine with this diluted mixture can lead to extreme engine damage in a VERY short time.

You should 1) add a manual fuel ON/OFF valve between the carb and fuel tank, and then 2) start using it religiously.

kkNKkyJh.jpg


#7

Scrubcadet10

Scrubcadet10

Born2Mow said:
This is a common issue when any fuel tank is mounted above the carburetor.

Gravity can/will force fuel to flow into the engine. (This may assisted by a tiny piece of trash stuck in the carb's float valve.) From there the fuel bypasses the piston rings and dilutes the engine oil in the sump. Such fuel systems are often fitted with manual or "automatic" fuel shut off valve. The problem is that when the automatic versions fail (go Open all the time), there is no way for the owner to tell... except that the dip stick will show an excess of fluid in the engine's sump.

► The carb's float bowl valve is not infallible. Even with the best of carbs, it is never a perfect seal.

► Running the engine with this diluted mixture can lead to extreme engine damage in a VERY short time.

You should 1) add a manual fuel ON/OFF valve between the carb and fuel tank, and then 2) start using it religiously.

kkNKkyJh.jpg
Click to expand...
Where's he gonna put that?


#8

B

Born2Mow

Scrubcadet10 said:
Where's he gonna put that?
Click to expand...
Hopefully in the fuel line between the tank and carb.


#9

R

Rivets

Born to Mow, do you realize that he has a tank mounted pulsajet carb. There is NO fuel line. Loch, the only way that this can happen twice is that you have oil which entered your tank somehow when you tipped the mower with the carb down. Run it a couple of times with fresh petrol and it should clear up. If it doesn’t post back and we’ll look for other solutions.


#10

L

LochlanR

Hi, I tipped the mower before I serviced it, after I tipped it, I cleaned the carb, the fuel tank, new diaphragm, and new oil by extraction (not tilting the mower).

edit: also has had brand new air filter and filter housing cleaned


#11

Scrubcadet10

Scrubcadet10

LochlanR said:
The carb looks like this, how would i go about changing the float needle?View attachment 66165
Click to expand...
Born2Mow said:
Hopefully in the fuel line between the tank and carb.
Click to expand...


#12

C

Curtisun

I had one similar come in with same problem fuel in oil. The carb was putting out too much fuel and was being sucked back through the crank case breather that connects to the carburetor. I replaced the carburetor and fixed it. Though the carburetor has no needle valve it does have neoprene gasket that is used to pump fuel. One of these has cracked and is allowing the fuel to flow back into the crankcase.
The other posters are assuming the tank is above the carburetor which the carb sets on top of the fuel tank and fuel is sucked up through the tube by the suction created in the crankcase on the neoprene gasket that is a pump. If this neoprene gasket has a small hole in it will put fuel into the oil.


#13

S

smallenginerepairs

The float in the carb may need adjusting. If the float in the car
LochlanR said:
Just bought and serviced a 35 Classic engine on a push mower, Started it and there was alot of blue smoke, although I did have to replace two back wheels so I had it on its side for about 20 mins. When i got it the oil looked to be over filled quite a bit so made sure to change it to the right amount before starting it. After starting, it took ages to burn off the oil until it eventually cleared. Used it to cut the grass and left it for a couple days. Just went to start it now and it shot out a cloud of blue smoke, its been kept upright and not on its side, checked the oil, its gone very dark gray after one use and smells a bit like petrol has mades its way into it.

What could be the issue? I assume it to be the piston rings or something relating to that.
Click to expand...
b does not shut off the fuel when the bowl is full it will enter the cylinder and drain down past the rings into the crankcase. Itcould also be your needle valve and seat, which are the parts that close the fuel port to the bowl. I hope this helps


#14

G

garyoldfart

When you put the mower on it's side ...Which side? Was the carb up?
If so the fuel runs straight into the crankcase


#15

S

smallenginerepairs

Rivets said:
Born to Mow, do you realize that he has a tank mounted pulsajet carb. There is NO fuel line. Loch, the only way that this can happen twice is that you have oil which entered your tank somehow when you tipped the mower with the carb down. Run it a couple of times with fresh petrol and it should clear up. If it doesn’t post back and we’ll look for other solutions.
Click to expand...
When tipping a push mower on it's side, if you go through this process first, no oil will enter the cylinder. First take ith pull rope in your hand and pull on it slowly, you will feel differences in resistance as you pull on the rope. When you get to the point of most resistance, the engine will be at top dead center and both intake and exhaust valves will be closed. Stop pulling on the rope at this time on your pull. With the engine at top dead center and both valves closed,no oil can enter your engine. At this time you can tip the mower on it's side and clean under your deck, take the blade off to sharpen, or whatever else you are about to do. I hope this helps you.


#16

V

v4n5b1

I've had this problem and it turned out to be oil in the muffler from being on it's side. Takes a lot of running before it burns off.


#17

B

bobrav517

Besides some on here under the impression he has a tank over the carb, which is wrong, it's a tank mounted carb, you're ignoring the fact it appears he has fuel building up in his crankcase, which could be a bad pump diaphragm in the carb. That's why they are called pulsajets. It pulsates using the crankcase vacuum to pump fuel. If corrupted, fuel can leak by back through into the engine crankcase, causing an overfilling situation, and heavy smoke upon starting. Solution is a new diaphragm pump, or because the carbs are very common and affordable, a new carb is probably the best idea.
All of that said, you could also have bad rings, allowing unburnt fuel to pass by the rings into the crankcase. If you have the means, you may want to check the compression. It should be between 80 and 120 psi. Have a great day!


#18

doug9694

doug9694

LochlanR said:
The carb looks like this, how would i go about changing the float needle?View attachment 66165
Click to expand...
The plastic over time warps and lets too much fuel past the diaphragm and gasket. Ebay or Amazon sells those inexpensively.


#19

B

bobrav517

doug9694 said:
The plastic over time warps and lets too much fuel past the diaphragm and gasket. Ebay or Amazon sells those inexpensively.
Click to expand...
Exactly


#20

L

LMPPLUS

With this carb setup it's really hard to get gas back into the crankcase oil, i'm wondering if you might have a fuel cap that the vent is plugged over pressuring the tank forcing gas out and into crankcase, just my 2 cents.


#21

L

LochlanR

I'll take yous through a step by step of what i've done:
- Tipped mower over for about 20 min to replace back wheels. 20 min on each side
- Mower was then left on its wheels while being serviced
- Cleaned fuel tank
- Cleaned carb
- New diaphragm
- Oil was extracted and replaced to the max and not over
- Mower was ran for a while, smoke cleared to a point where it wasn's smoking out my garden
- Cut lawn no issues
- 2 Days later, start it and it puffs big clouds of blue smoke out and continues to smoke
- Oil is now dark grey and smells a bit like petrol

I bought the mower as spares but was listed as only needing a back wheel as it had broken, so I don't know the condition of the internals. I can only assume that the piston rings are worn, so its letting oil past the top of the piston and burning it.


#22

C

Curtisun

The carb you showed sits on top of the fuel tank does it not?
Since it does not have a fuel line running to it, it has to use the vacuum to pull fuel up through the tube going down into the tank. So it has to have a diaphragm and that diaphragm has to have a hole somewhere in it leaking by. The only two routes fuel can get into the oil is:
1. Through the carburetor to crankcase vent port.
2. Through the carburetor to the intake through the intake valve to the piston then by the rings.
Since The mower I presume sets level when it gets oil in the fuel it is either being syphoned into the oil by the crankcase or by the mower setting at an angle. It dos no matter if the angle is left, right forward or backwards.
If you have a full Tank of fuel and leave mower setting on an incline it can and will drain back through the carb to the crankcase oil either through the jet that regulates the amount of fuel or through the vent.
1691872961190.png


#23

C

Curtisun

LochlanR said:
I'll take yous through a step by step of what i've done:
- Tipped mower over for about 20 min to replace back wheels. 20 min on each side
- Mower was then left on its wheels while being serviced
- Cleaned fuel tank
- Cleaned carb
- New diaphragm
- Oil was extracted and replaced to the max and not over
- Mower was ran for a while, smoke cleared to a point where it wasn's smoking out my garden
- Cut lawn no issues
- 2 Days later, start it and it puffs big clouds of blue smoke out and continues to smoke
- Oil is now dark grey and smells a bit like petrol

I bought the mower as spares but was listed as only needing a back wheel as it had broken, so I don't know the condition of the internals. I can only assume that the piston rings are worn, so its letting oil past the top of the piston and burning it.
Click to expand...
The flappers if they do not seat good or the diaphragm is not next to the carb then the flappers will allow fuel to leak by if the mower is not setting level. Btw worn piston rings will not matter about fuel getting into the oil. New rings will not stop the liquid fuel.


#24

M

MartinR

LochlanR said:
Just bought and serviced a 35 Classic engine on a push mower, Started it and there was alot of blue smoke, although I did have to replace two back wheels so I had it on its side for about 20 mins. When i got it the oil looked to be over filled quite a bit so made sure to change it to the right amount before starting it. After starting, it took ages to burn off the oil until it eventually cleared. Used it to cut the grass and left it for a couple days. Just went to start it now and it shot out a cloud of blue smoke, its been kept upright and not on its side, checked the oil, its gone very dark gray after one use and smells a bit like petrol has mades its way into it.

What could be the issue? I assume it to be the piston rings or something relating to that.
Click to expand...
When you put the mower on its side did you have the carb on the upper side? With the oil as you describe it you need to change it ASAP.


#25

S

stihlmania

LochlanR said:
Just bought and serviced a 35 Classic engine on a push mower, Started it and there was alot of blue smoke, although I did have to replace two back wheels so I had it on its side for about 20 mins. When i got it the oil looked to be over filled quite a bit so made sure to change it to the right amount before starting it. After starting, it took ages to burn off the oil until it eventually cleared. Used it to cut the grass and left it for a couple days. Just went to start it now and it shot out a cloud of blue smoke, its been kept upright and not on its side, checked the oil, its gone very dark gray after one use and smells a bit like petrol has mades its way into it.

What could be the issue? I assume it to be the piston rings or something relating to that.
Click to expand...
Have you run it for sometime to see if smoke goes away? Also a second oil change I find is necessary to clean up oil.


#26

P

PGB1

My 35 classic did the same as yours, LochlinR. I changed the carburetor diaphragm (the top gasket looking thing in your photo) and it solved the problem for about 4 years. When it did it again, I changed the diaphragm again & the problem hasn't yet returned. It's been another 4 years. The diaphragm may last longer if you buy a real one. I bought eBay clones.

I'm by no means a mechanic, but examining the old versus new diaphragm showed that the old was wrinkled. I suspect alcohol in the fuel caused that.

I hope this helps,
Paul
PS: There's no place on the 35 Classic to put the shut-off that Born2Mow mentioned, but I have them on all of my gasoline equipment that has float bowl carburetors. They're a great aggrivation saver. I also have in-line tees with valves on seldom used equipment so that I may readily drain the fuel from the tank after the engine cools.


#27

C

Curtisun

PGB1 said:
My 35 classic did the same as yours, LochlinR. I changed the carburetor diaphragm (the top gasket looking thing in your photo) and it solved the problem for about 4 years. When it did it again, I changed the diaphragm again & the problem hasn't yet returned. It's been another 4 years. The diaphragm may last longer if you buy a real one. I bought eBay clones.

I'm by no means a mechanic, but examining the old versus new diaphragm showed that the old was wrinkled. I suspect alcohol in the fuel caused that.

I hope this helps,
Paul
PS: There's no place on the 35 Classic to put the shut-off that Born2Mow mentioned, but I have them on all of my gasoline equipment that has float bowl carburetors. They're a great aggrivation saver. I also have in-line tees with valves on seldom used equipment so that I may readily drain the fuel from the tank after the engine cools.
Click to expand...
Your suspicion about the alcohol is correct it will degrade the diaphragm over time and about it not having a fuel line. This carb does not have a float but uses the jet to regulate flow. I believe one of those two flappers allow the excess fuel to return to the tank and the other acts as pump valve. If either leak by or you have a hole in that diaphragm it will put fuel into the oil while it is running or setting at an angle. I do not remember having a classic in my shop, but I have had some with the same carb.


#28

thesilentone

thesilentone

The carb is mounted directly on the tank, (on the side of the engine) and is a diaphragm pump. No float valve, no place for a tap !

Sounds to me like the breather valve is not working properly, take it off and check.


#29

C

Curtisun

There is one other thing that comes to mind about these type carbs. If memory serves me correctly, they are made of high temp polystyrene plastic and when plastic gets old it can crack. If this carb has a crack in it were the fuel flows, then that could also be the problem.


#30

F

first pull

LochlanR said:
Just bought and serviced a 35 Classic engine on a push mower, Started it and there was alot of blue smoke, although I did have to replace two back wheels so I had it on its side for about 20 mins. When i got it the oil looked to be over filled quite a bit so made sure to change it to the right amount before starting it. After starting, it took ages to burn off the oil until it eventually cleared. Used it to cut the grass and left it for a couple days. Just went to start it now and it shot out a cloud of blue smoke, its been kept upright and not on its side, checked the oil, its gone very dark gray after one use and smells a bit like petrol has mades its way into it.

What could be the issue? I assume it to be the piston rings or something relating to that.
Click to expand...
Could be valve guides of valve gummed up with carbon, not allowing it to seat properly


#31

doug9694

doug9694

LMPPLUS said:
With this carb setup it's really hard to get gas back into the crankcase oil, i'm wondering if you might have a fuel cap that the vent is plugged over pressuring the tank forcing gas out and into crankcase, just my 2 cents.
Click to expand...
In my experience that happens with small trimmers and blowers, ect. The opposite is what I see. The engine running creates a vacuum and quits from fuel starvation.


#32

doug9694

doug9694

first pull said:
Could be valve guides of valve gummed up with carbon, not allowing it to seat properly
Click to expand...
Gray oil is from water. Maybe some was in the tank or can used to fill it. Also if left in the rain or spray.


#33

B

Boggie123

Hi LochlanR.
Did you get to the bottom of this? I had my mower (a Hayter Hobby 41 with a Briggs and Stratton classic 150cc, similar to yours) on its side for a while too. I was swapping the engine into another chassis and had removed the fuel tank, but not the oil. Now, with the engine fitted into the restored chassis and serviced, I started the engine and it smokes like hell (it was running fine before the swap) and there is a little oil coming out of the exhaust. Does tipping these engines on its side somehow get oil into the exhaust port (and in your case, also fuel into the oil)? Did the smoke clear after more use?
Thanks, B.


#34

P

PGB1

For what it is worth, I have a very old Briggs & Stratton Classic 35. I'm no small engine person, but the blue smoke I've had.

Cause One:
Once I loaned the machine it's on and the borrower was kind enough to change the oil- overfilling it. After getting the oil to proper level, it took hours and hours or run time for it to stop with the blue smoke.

Cause Two:
Another time or two or three or more with blue smoke and oil in the fuel it turned out the be the diaphragm between the tank and the carburetor. Ethanol in the gasoline damages the gasket, it wrinkles and then fuel floods into the engine. Eventually it gets to the oil & dilutes it. When diluted, the now too full oil gets burned with fuel causing blue smoke. Expect many hours of run time to clear the smoke.

The gaskets are about a dollar on places like eBay and a few dollars locally. Changing it is perhaps a 20 minute project. I change it annually as habit.

Paul


#35

B

Boggie123

Thanks Paul.
In my case, it was oil in the exhaust silencer (muffler). I took it off, started the engine and ran it for a couple of minutes. No smoke. So, I flushed the silencer with petrol, then hot soapy water, thoroughly dried it off and, seeing as it was off the engine, prepped it and applied a coat of high temperature paint. I refitted it and started the engine. No smoke!

What seems to have happened is that when I tipped the mower on its side by about 45° (exhaust side down) to remove the engine as part of the restoration process, oil flowed into the silencer (possibly via the open exhaust valve?), even though I had drained the engine via the sump plug. From now on, I will only tip the engine backwards (spark plug up) as oil can't get into the exhaust or inlet/carb that scenario.

One note of caution regarding running an engine with high oil level (e.g. to burn off the excess) - A mechanic friend some years ago told me that high oil levels can mean that the crank bearing journals and conrods are splashing about in the oil, and cause lots of air bubbles in the oil. These are then sucked up by the oil pump pickup pipe and with prolonged use, can cause engine wear damage. He was talking about an engineer's report on a car engine failure, so I am not sure how that relates to single cylinder vertical mower engines, but they do have a sump where the crankshaft spins, so it is probably true for them too. I would recommend lowering oil level by sucking some out through the filler hole, with a pump or even a thin turkey baster, rather than running the engine for quite a while to burn off the excess.


#36

P

PGB1

Boggie123 said:
Thanks Paul.
In my case, it was oil in the exhaust silencer (muffler). I took it off, started the engine and ran it for a couple of minutes. No smoke. So, I flushed the silencer with petrol, then hot soapy water, thoroughly dried it off and, seeing as it was off the engine, prepped it and applied a coat of high temperature paint. I refitted it and started the engine. No smoke!

What seems to have happened is that when I tipped the mower on its side by about 45° (exhaust side down) to remove the engine as part of the restoration process, oil flowed into the silencer (possibly via the open exhaust valve?), even though I had drained the engine via the sump plug. From now on, I will only tip the engine backwards (spark plug up) as oil can't get into the exhaust or inlet/carb that scenario.

One note of caution regarding running an engine with high oil level (e.g. to burn off the excess) - A mechanic friend some years ago told me that high oil levels can mean that the crank bearing journals and conrods are splashing about in the oil, and cause lots of air bubbles in the oil. These are then sucked up by the oil pump pickup pipe and with prolonged use, can cause engine wear damage. He was talking about an engineer's report on a car engine failure, so I am not sure how that relates to single cylinder vertical mower engines, but they do have a sump where the crankshaft spins, so it is probably true for them too. I would recommend lowering oil level by sucking some out through the filler hole, with a pump or even a thin turkey baster, rather than running the engine for quite a while to burn off the excess.
Click to expand...
I'm glad it worked out & thanks for sharing what the cause was!

Thanks, too, for advising about over-filling the oil.

Happy Mowing!
Paul


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