Carb leak filled cylinder with gas

[Auto Doc's]

I bought a used machine with a B&S 305 CC 1350 series OHV motor. It ran like a top, until I brought it home, filled the gas tank, and left it for a day. The carb leaked fuel all over the floor. After installing a carb kit, and trying to restart, it locked up on the compression stroke: turns out the cylinder was completely full of fuel. I could rotate it backwards with the crankshaft pulley bolt, and after working it back and forth for some time, the gas cleared out of the muffler and I could rotate it. Then I restarted, and it ran super rough and belched white smoke. I checked the oil, and found that a half quart of fuel had gotten into the oil, it was now nearly twice too full. I drained the contaminated oil, flushed the crankcase a couple times, and refilled to the right level. Still runs terrible and blows tons of smoke. I turned the crankcase breather around so no oil mist could get from the valve cover to the air intake, with no success. Every once in a while it revs almost to full RPM and runs nearly clean for a few seconds, then starts misfiring and smoking like crazy again. Thinking there must be some reservoir of oil under the valve cover, or in the intake manifold, or maybe I installed something wrong on the carb, I dismantled the whole thing, and everything looks clean and correct. There are no oil pools except by the valve guides (just above the manifolds), about 1/2 tsp in each. I cleaned that out, reassembled, and tried again. It started rough, then cleaned up and ran so-so, with not much smoke, but instead of cleaning out and running normal, it started running worse and worse until it finally died.
My question is whether it's possible that filling the cylinder with liquid fuel and then running it out past the valves could have caused permanent damage, for example to the valve guides, that then allows raw oil into the intake manifold or cylinder? Or whether running even briefly with gas-diluted oil could have done something permanent?

A carburetor "overhaul" with new parts does not always fix the carburetor.

One thing that is often overlooked is cleaning the float needle seat with a Q-tip and a little carburetor spray. I've learned that over the years, especially dealing with ATVs and 4-wheelers. The same problem happens with mower engines, but not as common.

 

[oldntired55]

No telling how many times the previous owner ran it with severely diluted gas. Got impatient and sold it to you. Fair to say?

So it could have -10w 0.3 oil in it when you got it. Then you did your best trying to get her running. Fair to say?

Very well could of trashed the engine. Hope it turns out good for you.

What I would of done is pull the oil stick. Smell for fuel before ever BUYING/trying to start it. Prior to EVERY MOW, this is A MUST. Mainly keeping the oil on the FULL MARK for EVERY MOW.

Being a used machine, EVERYTHING on that mower in my opinion, is suspect. Meaning I would go through the entire machine making sure she is tip top before trying to use it.

Similar to used vehicles. All fluids get dumped. Power steering, coolant and rear end fluid if applicable. Maybe 1% of people change power steering juice if that. Normally it's black as the engine oil. Brake fluid the same.

Agree with Star Tech and Rivets. Fix the needle/seat and pressure test at 7psi for 30+ minutes. Don't use the engine till this is fixed. Then make sure you have oil ONLY in the sump.

just a quick question, when pressure testing with carb invertedm is it done with just the weight of the float holding needle shut??

 

[David40]

Does your fuel line have a simple 1/2 turn gas shutoff valve?
If not, install one for a couple bucks.
When your done using the machine shut off the valve and let the carb run empty to stop the engine.
Next time you use it just open the valve and crank the engine with the electric starter till it starts and runs.
You may or may not need to use the manual choke if it has one.
It sounds like the carb is the real problem.
Some carbs have an electric shutoff valve for fuel in the bottom of the bowl that don't work.

I have had this problem many times over the years, so whenever I purchase a new machine I install a fuel shut off valve and only open it when the machine is in use. It's a fast, easy, cheap solution.

 

[glyn1718]

I bought a used machine with a B&S 305 CC 1350 series OHV motor. It ran like a top, until I brought it home, filled the gas tank, and left it for a day. The carb leaked fuel all over the floor. After installing a carb kit, and trying to restart, it locked up on the compression stroke: turns out the cylinder was completely full of fuel. I could rotate it backwards with the crankshaft pulley bolt, and after working it back and forth for some time, the gas cleared out of the muffler and I could rotate it. Then I restarted, and it ran super rough and belched white smoke. I checked the oil, and found that a half quart of fuel had gotten into the oil, it was now nearly twice too full. I drained the contaminated oil, flushed the crankcase a couple times, and refilled to the right level. Still runs terrible and blows tons of smoke. I turned the crankcase breather around so no oil mist could get from the valve cover to the air intake, with no success. Every once in a while it revs almost to full RPM and runs nearly clean for a few seconds, then starts misfiring and smoking like crazy again. Thinking there must be some reservoir of oil under the valve cover, or in the intake manifold, or maybe I installed something wrong on the carb, I dismantled the whole thing, and everything looks clean and correct. There are no oil pools except by the valve guides (just above the manifolds), about 1/2 tsp in each. I cleaned that out, reassembled, and tried again. It started rough, then cleaned up and ran so-so, with not much smoke, but instead of cleaning out and running normal, it started running worse and worse until it finally died.
My question is whether it's possible that filling the cylinder with liquid fuel and then running it out past the valves could have caused permanent damage, for example to the valve guides, that then allows raw oil into the intake manifold or cylinder? Or whether running even briefly with gas-diluted oil could have done something permanent?

You will have lots of oil in the exhaust, which starts to burn off (smoke,) when it gets hot. Fix the leaking carb float needle seating ( you can simply check by assembling the carb and blow into the fuel inlet. Air should pass. Turn the carb upside down and you should not be able to blow air in. ) and putting clean oil in will allow it to run to burn off all the oil in the exhaust. Then I would change oil again and you should be good to go.

 

[mechanizm]

Never start or turn-over an engine that has been flooded with gas because the gas washes the oil off of the cylinders. The rings will destroy the cylinder wall.

pull the plugs, squirt lots of oil in the cylinders, let set overnight then crank the engine by hand without plugs to re-lube the cylinder wall.

 

[Auto Doc's]

just a quick question, when pressure testing with carb invertedm is it done with just the weight of the float holding needle shut??

Hello O.,

To test a carburetor seat, I use a handheld vacuum pump with the carburetor turned upside down and just a little bit of vacuum applied. If it cannot hold the vacuum for a couple of minutes, the needle is leaking. Note: Make sure the handheld vacuum pump and line used works correctly before performing the test. A leaking vacuum pump or line will give you a false leak test.

Another method is using clear soft line or large weed eater fuel line attached to the carburetor fuel inlet and mount the carburetor If needed), so it is upright, then fill the transparent line with fuel using a dropper/syringe or similar device. Let it sit and watch the fuel level in the line after the fuel bowl is filled. It will be obvious if it is leaking at the needle, because the level in the line will keep going down.

On a side note: People are often confused if there is an electric solenoid on the bowl of a carburetor.... That solenoid is not a (true) fuel "shutoff" It is more of a fuel restrictor that keeps excess fuel from being drawn in has an engine winds down after the ignition is shut off. It prevents backfires due to fuel making its way into a hot exhaust. The formal name of this device is referred to as an "after-fire" or anti-backfire solenoid.

Inside the carburetor, think of the float as a "bobber". It constantly controls fuel flow as the engine demand increases or decreases. When an engine is shut down, the float bowl will be full and that is what holds the needle closed to the seat. It is not always a guarantee the fuel bowl will remain full due to fuel evaporation and temperature changes.

The true method to prevent problems is to install a simple manual fuel shutoff in the line just before the carburetor.

 

[tcpuccio1]

that actually called hyro-locking it. a liquid can't de compressed thus it locked it up solid. I think it's safe to say this was not a new problem that cropped up on you. it was on going. and it keeps over fueling this the fast rev up and the smoke if it's over fueling that much it will not have black smoke that you would normally see from a rich condition you have an overly rich condition will be white smoke. the needle and seat are not sealing of the float is not "floating" pretty simple go through the carb again and relace the needle and seat and seat not sure on that model if the seat is a rubber o-ring or part of the nylon float contraption there is a seal between that, and the carb body look at that as well. just a screw brass or plastic seat. probably a kit like this is what you need double check model and serial # https://www.walmart.com/ip/NEW-Carb...1?wmlspartner=wlpa&selectedSellerId=101098489
there are plenty of video's on youtube on how to fix these. this is what you have and in the video the dude mentions hydro lock so it's right in your wheel house.

and
as for permanent damage i doubt it. one thing would be if the gas washed down the cylinder walls then you going to have some oil consumption issues. get it running correctly use it couple of times and dump the oil and keep an eye on it. I personally would not use synthetic oil in it during you evaluation process after a couple of changes and it's not burning oil then switch it over to full synthetic oil any kind of name brand is fine. Personally I use NAPA brand oil which is rebadged Valvoline. where I work, we own a NAPA store, so I get it at at discount.

 

[Auto Doc's]

Never start or turn-over an engine that has been flooded with gas because the gas washes the oil off of the cylinders. The rings will destroy the cylinder wall.

pull the plugs, squirt lots of oil in the cylinders, let set overnight then crank the engine by hand without plugs to re-lube the cylinder wall.

Hello M.,

I understand what you are saying, but people seldom want to wait overnight. I would not recommend using "lots of oil" as you suggest because the oil may not seep enough past the rings.

To some, that could mean fill the cylinder with oil and then try to crank it up. That would create a hydro lock condition. Instead, a couple of shots of WD-40 spray will do the trick.

 

[oldntired55]

Hello O.,

To test a carburetor seat, I use a handheld vacuum pump with the carburetor turned upside down and just a little bit of vacuum applied. If it cannot hold the vacuum for a couple of minutes, the needle is leaking. Note: Make sure the handheld vacuum pump and line used works correctly before performing the test. A leaking vacuum pump or line will give you a false leak test.

Another method is using clear soft line or large weed eater fuel line attached to the carburetor fuel inlet and mount the carburetor If needed), so it is upright, then fill the transparent line with fuel using a dropper/syringe or similar device. Let it sit and watch the fuel level in the line after the fuel bowl is filled. It will be obvious if it is leaking at the needle, because the level in the line will keep going down.

On a side note: People are often confused if there is an electric solenoid on the bowl of a carburetor.... That solenoid is not a (true) fuel "shutoff" It is more of a fuel restrictor that keeps excess fuel from being drawn in has an engine winds down after the ignition is shut off. It prevents backfires due to fuel making its way into a hot exhaust. The formal name of this device is referred to as an "after-fire" or anti-backfire solenoid.

Inside the carburetor, think of the float as a "bobber". It constantly controls fuel flow as the engine demand increases or decreases. When an engine is shut down, the float bowl will be full and that is what holds the needle closed to the seat. It is not always a guarantee the fuel bowl will remain full due to fuel evaporation and temperature changes.

The true method to prevent problems is to install a simple manual fuel shutoff in the line just before the carburetor.

i have tested every carb ive done with my vacuum pump, my question was.. when Pressure testing, is the weight of the float all that is needed with carb inverted?

 

[Gord Baker]

I bought a used machine with a B&S 305 CC 1350 series OHV motor. It ran like a top, until I brought it home, filled the gas tank, and left it for a day. The carb leaked fuel all over the floor. After installing a carb kit, and trying to restart, it locked up on the compression stroke: turns out the cylinder was completely full of fuel. I could rotate it backwards with the crankshaft pulley bolt, and after working it back and forth for some time, the gas cleared out of the muffler and I could rotate it. Then I restarted, and it ran super rough and belched white smoke. I checked the oil, and found that a half quart of fuel had gotten into the oil, it was now nearly twice too full. I drained the contaminated oil, flushed the crankcase a couple times, and refilled to the right level. Still runs terrible and blows tons of smoke. I turned the crankcase breather around so no oil mist could get from the valve cover to the air intake, with no success. Every once in a while it revs almost to full RPM and runs nearly clean for a few seconds, then starts misfiring and smoking like crazy again. Thinking there must be some reservoir of oil under the valve cover, or in the intake manifold, or maybe I installed something wrong on the carb, I dismantled the whole thing, and everything looks clean and correct. There are no oil pools except by the valve guides (just above the manifolds), about 1/2 tsp in each. I cleaned that out, reassembled, and tried again. It started rough, then cleaned up and ran so-so, with not much smoke, but instead of cleaning out and running normal, it started running worse and worse until it finally died.
My question is whether it's possible that filling the cylinder with liquid fuel and then running it out past the valves could have caused permanent damage, for example to the valve guides, that then allows raw oil into the intake manifold or cylinder? Or whether running even briefly with gas-diluted oil could have done something permanent?

Do the Simple thiings first. You were correct in dumping the Crankcase oil. Some residual oilmix may remain in the Intake or Exhaust manifold. Install a fuel shut off valve. Change Spark Plug, perhaps to a hotter one. Did you change Needle and Seat? That is why fuel leaked. Check Valve lash 0.004-6 and run it.