gasoline in crankcase oil?

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  #1  
Old 05-08-03, 10:54 PM
garydamwright
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gasoline in crankcase oil?

My MTD riding lawn mower (16.5 HP Briggs twin, commercial) has been running fine until recently. After I filled the gas tank in preparation for use, the engine started up OK, but ran for only a few seconds - there was a puff of blue smoke from the exhaust, it died, and then would not start. The engine turns over fine, but does not offer to fire. I removed the air filter (which was dirty), and I noticed the smell of gasoline and that the intake area was wet with gas. Because of the strong smell of gas, I did not test for spark.

Thinking I had flooded the engine, I left the air filter off over night hoping it would dry out, but the next day it still wouldn't start. Then I noticed the gas tank was half empty. Since I couldn't smell or see gas on the garage floor, I pulled the dipstick which showed too much volume, too little color, and smelled of gas - also the dipstick ignited easily and burned like a torch (I havent tested the dipstick from my car, but I'm guessing pure oil would be harder to light).

What would allow the gasoline to drain or siphon into the crankcase? Would it be stupid to just change the oil and try using the mower again or would I be asking for trouble? Aside from the explosion issue, I'm guessing oil diluted with gasoline does not protect very well, and the engine life would be significantly shortened if the problem returned while I was mowing?

Because I'll have to rent a trailer to get this thing to the shop, any do it yourself testing or repair tips would be appreciated.

Thanks,
-GW
 
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  #2  
Old 05-09-03, 12:47 AM
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Ok. First the needle valve on the float isn't sealing completely due to a possibly needed float adjustment or trash stuck to the needle valve seat. This is allowing gas to flow past the needle valve and into the cylinder where it eventually leaks past the rings into the crankcase mixing with the oil. Then the oil level rises and could flow through the crankcase ventelator and flow into the carburetor allowing oil to be burned in the cylinder. This might explain the puff of blue smoke. When the gas gets in the oil, don't run it. Engine damage would occur. To fix this entire problem you could take the carburetor appart and clean it or you could buy a kit to rebuild it, but the cheapest, easiest, and best way to fix it is to buy a fuel shutoff valve. They only cost about $1. Just cut the fuel line coming from the gas tank and slip the two ends on each side of the plactic valve. Just make sure to shut the gas off when your finished with it for the day. Also, make sure to change the oil before starting it. Hope this helps!!!!!!
 
  #3  
Old 05-10-03, 01:40 AM
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Hello Gary!

I agree that the needle in the carb is not sealing. You will need to repair it though, as the shutoff valve will not solve the problem when the engine is running. It just keeps the engine from flooding when it is off.

Remove the air filter housing and the top of the carb. From there, you can remove the float and see the needle. Replace the needle, and swab out the seat where the needle inserts with a Q-tip soaked with carb cleaner, and replace the float if it has gas sloshing in it. Then reassemble and change the oil.

Let us know how it goes!
 
  #4  
Old 05-11-03, 04:39 AM
garydamwright
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re: gas in oil

Thanks to mower17 and cheese for your helpful advice.

So far, the shut off valve and oil change have got me up and running, at least temporaily. There was quite a bit of blue smoke from the exhaust for the first few minutes after I first got it started, but that cleared up, and now runs great, so I guess I didn't ruin it. I'd like to try the more permanent repairs suggested by cheese, but I am a little apprehensive about working on a carb - aren't they in the same catagory as wrist watches and brain surgery when it comes to do it your self repairs?

I might first try to find an exploded diagram of my carb on the web to see what I'd be getting into. If I ask my local small engine repair shop for a 'rebuild kit' will it have everything I need in it? Would a new float need some kind of adjustment after installation? Do I need to have some kind of gaskets or sealers on hand? As you can tell, small engine repair is new to me. I wish I had spent more time in my grandpa's mower shop when I was a boy - he was a pro.

Thanks,
-GW
 
  #5  
Old 05-11-03, 11:18 AM
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Rebuilding a carburetor isn't that hard. Just make sure you clean it very good. If you get a rebuild kit, it will have everything you need. To disassemble the carburetor, just remover the small screws/bolts holding it together. After you remove these, then the fuel bowl will come off. Then slide out the small pin holding the float in place. Then remove the float, the needle valve will come with it. Remember how this all goes. Then remove the needle valve on the outside of the carburetor and any jets inside the carburetor. You will need a small flat blade screwdriver to unscrew them. Basically, you just want to strip the carburetor down so you can clean everything. Then, clean the heck out of everything, especially every small hole. Then install the new gaskets and needle valves and put it all back together. It's not that hard. There is probably just 4 or 5 things to remove, so, if you use diagrams, you shouldn't have a problem. Good luck.
 
  #6  
Old 05-11-03, 08:19 PM
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Not hard at all. It is a very simple carburetor, and I know it like the back of my hand, so if you run into trouble, We'll be here to help. Just remove the air filter cover, air filter, the three 5/16" head screws that hold the bottom half of the air filter box onto the carb, then you see the carb in it's entirety.

Blow any dirt away and off of the carb, or spray it off with carb cleaner. Remove the choke cable (held on with one 5/16" head screw). Then, remove the 4 screws around the top of the carb at each corner. Be careful not to dorp any of these down the carb throat, but if you do, use a magnet to get it out.

Once these screws are removed, you can pull the top off of the carb and the float and needle will come out with it. Look where the float goes in the bottom half of the carb (the bowl). Clean out any trash, debris, rust, etc... Remove the drain plug on the side if you need to, to wash out the trash.

Pull the hinge pin that holds the float onto the carb top. Lift the float out and the needle will come out with it. Replace that needle, soak a Q-tip with carb cleaner and swab the area that the needle goes into to clean it well. Check the float by shaking it near your ear. If you hear gas sloshing inside it, replace it. Then reassemble the float and needle to the top of the carb. Make sure the float travels freely up and down without using any pressure. The newer carbs with plastic floats often have to be filed on the inside edges of the float hangers to allow better clearance to keep the float from rubbing them. If the top gasket tore, or looks pretty bad, replace it too. Then reassemble the carb and go!

There are very few pieces to lose, and the thing can pretty much only go back together one way, so give it a shot! I do these carbs in 15 minutes, so, this being your first time, you should still be able to do it in an hour.

Keep us posted!
 
  #7  
Old 03-12-07, 09:18 AM
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Gas in crankcase

Have same problem. 9hp B&S Vanguard engine on a generator.Ran fine 6 months ago. Started briefly, then quit. Went to check oil. Gas spewed out. Emptied 3 litres out !
So a thorough carb cleaning is in order I gather.
Are the carb "service kits" standard for B&S engines ?
 
  #8  
Old 03-12-07, 02:29 PM
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Welcome DEEDOCKTUH! We should be well able to help you out here. For future troubles let me suggest starting your own thread for each machine you have issues with. But, to answer your question, there is not necessarily a generic carburetor rebuild kit for Briggs engines. Many Briggs and especially the Vanguard series could potentially have more than one carburetor option installed from the factory and in many cases the ID numbers alone will not tell us (technicians) what you have specifically on YOUR engine but we do need to at least have this information to get started on your trouble. So, post back, in this thread, with the model, type and code numbers from your engine. And, as a rule, we'd like to know the specifics on the unit to which it is attached as far as make, model and serial of such. So, do the same here as well...Engine ID numbers and chassis ID numbers, please.
 
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