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Can someone explain the gas in oil thing?

  • Thread starter Thread starter brand new bike zealot
  • Start date Start date
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brand new bike zealot

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I had a carb overflow like crazy a while back and spew gas out the valve on the bottom all over the motor. (No overflow lines at that point, has since been rectified) After learning about the gas in oil thing from this incredible site, I did the smell test and lo and behold, gas in oil. So how does it get into the crankcase? I haven't taken my carbs aoart yet, so I don't entirely understand how the fuel enters the combustion chamber, but is it overflowing onto the pistons and down past the rings?

On a sidenote.. The gas cleaned off my oil level window to almost as new clarity! Before this I couldn't see through it at all! http://www.thegsresources.com/_forum/images/smilies/eusa_dance.gif
 
A bad petcock can allow gas to escape out of the tank into your carbs. In the carbs you have a float needle and seat. When the float bowl is full the float floats and closes the needle valve and does not allow gas to flow any further. If the float needle and seat are not seating (closing) due to dirt, rust or worn out parts the fuel continues to flow up out of the carbs into your cumbustion chamber, past your piston rings and into your crankcase and hence a clean oil level window.
 
For this to happen, you must have both a defective petcock & defective needle & seat or (seats).
 
rphillips said:
For this to happen, you must have both a defective petcock & defective needle & seat or (seats).
Click to expand...

Or petcock was left in the Prime position which allows the gas to flow at all times.

At any rate, remove the drain plug on the bottom of the engine and change the oil (and at least, drain the oil out of the filter cavity if not change the filter entirely).
 
brand new: gas like any liquid will seek the lowest level. since our bikes are gravity fed, the gas if un obstructed will run to the lowest point in the bike which is the the crankcase. You have a few areas that control the flow as the others noted;
the fuel petcock, the fuel valve , the float and needle valve.
If the gas makes it past all of these then it flows in to the combustion chamber, on to the top of the piston, past the rings and in to the oil. downhill all the way.
good luck and take care, ikazuki
 
thanks for the replies guys, that makes all makes sense now. I've changed the oil with some cheap stuff and will do an oil and filter in a bit with some good stuff. When I had my flood issue, the valve was on run. I'm basically positive it was a stuck float valve, bit of crud or something. I pulled the vacuum line off the petcock and ran the bike until it stalled out. Does this suggest the petcock is working fine? When I reconnected the vacuum line the incoming fuel flushed out whatever was clogging the valve to the bottom of the bowl, to be delt with next rebuild.

Is there a better way to check the petcock? Well, I'm sure there is, basically I'm wondering if my test was sound...
 
The float needles are not designed to hold back the flow of gasoline forever. Even if they're perfect, gas can still trickle through over the course of a few days if the petcock is left in prime or has some other problem.

Petcocks also fail because the the very thin vacuum diaphragm inside is 25 or so years old, and almost inevitably develops a leak over long spans of time. This can also allow gas to seep through, flow into the vacuum fitting, into the cylinder, etc.

I think I'll just put the following in my sig so I can stop typing it:
"Petcocks do not last forever. Every GS needs a new petcock every 20-25 years. Buy a complete new Suzuki petcock (the rebuild kits are usually junk) and forget about it for another 20 years. There are no safe workarounds or cheap fixes. The same applies to intake boots and o-rings."
 
If your petcock is fine then it is your needle valve seat 0-rings.They are easy to replace and it will fix your problem.i just did mine a couple of months ago.i was getting some gas in the airbox also and dripping out the airbox drain hose.
 
bwringer said:
The float needles are not designed to hold back the flow of gasoline forever. Even if they're perfect, gas can still trickle through over the course of a few days if the petcock is left in prime or has some other problem.

Petcocks also fail because the the very thin vacuum diaphragm inside is 25 or so years old, and almost inevitably develops a leak over long spans of time. This can also allow gas to seep through, flow into the vacuum fitting, into the cylinder, etc.

I think I'll just put the following in my sig so I can stop typing it:
"Petcocks do not last forever. Every GS needs a new petcock every 20-25 years. Buy a complete new Suzuki petcock (the rebuild kits are usually junk) and forget about it for another 20 years. There are no safe workarounds or cheap fixes. The same applies to intake boots and o-rings."
Click to expand...

tconroy said:
If your petcock is fine then it is your needle valve seat 0-rings.They are easy to replace and it will fix your problem.i just did mine a couple of months ago.i was getting some gas in the airbox also and dripping out the airbox drain hose.
Click to expand...

I wish I would've gotten these mssages clear before I went through this whole mess. I never did have gas in the oil... or gas flowing out the airbox. But I had a very strong odor of gas, bothered everyone around. The only liquid gas I ever found anywhere, even after sitting for a week, was very small amounts pooling up in the cylinder fins.

Maybe a few drips were coming from the hard and stiff intake boots. Anyway, I tried a petcock rebuild kit, half the guys here said it worked, half said it didn't. It was cheap, so I tried it... didn't work for me.
So I bought 4 carb rebuild kits (K&L, or Keyster?) - Robert Barrs 0-rings - the "boots" going forward and backward from the 4 carbs - a new Suzuki petcock. I did the petcock and paid a local m/c mechanic I trust to do the rest.
It worked out... probably lot more was done than was needed, but there was no clear way of knowing that before you get into the whole thing.
My 850 ran good before, and it runs good now... just NO smell of gas anymore \\:D/
 
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