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Gas in crankcase

5K views 15 replies 4 participants last post by  Down 
#1 ·
I have read several posts regarding my problem, but still am unsure of the cause. I discovered that about 2 gallons of gas decided it wanted to relocate into the crankcase while the bike was sitting. I took apart the petcock, there was some corrosion on it. Cleaned that up. Checked the float, seems fine. I changed the oil, plugs and air cleaner and ran the bike for a few miles at low speeds. Changed the oil again and got back an extra 1/2 gallon of gas mixed in with my oil. The plugs are already as black as the paint on my bike with only about 6 miles on them. My question is what would cause fuel to seep into the motor in such mass quantities? Vacuum line? Float Valve? I can't see how the could happen from sitting. I had the fuel shut off. I plan on pulling the carb again tonight. I am open for suggestions. Thanks in advance for any advice.
 
#2 ·
The petcock at the fuel tank is vacuum controlled to shut off fuel when the engine stops. If this valve fails to stop the fuel, the weight of the fuel sitting on the needle seat in the carb can overwhelm it and cause the bowl to overfill and dump into the crankcase.

The petcock can be rebuilt or replaced, and in the meantime shut it off (lever pointing forward) when parking your bike.
 
#3 ·
The petcock at the fuel tank is vacuum controlled to shut off fuel when the engine stops. If this valve fails to stop the fuel, the weight of the fuel sitting on the needle seat in the carb can overwhelm it and cause the bowl to overfill and dump into the crankcase.

The petcock can be rebuilt or replaced, and in the meantime shut it off (lever pointing forward) when parking your bike.
The fuel was shut off when it happened for the second time. It was left on when it happened the first time. I have been leaving the fuel line disconnected from the petcock until I get it fix whatever the problem is.
 
#4 ·
Unhook the vacuum line from the petcock and see if any fuel is present at the fitting or in the hose.

Also, with both hoses disconnected from the petcock, move the lever from ON (down) to OFF (forward) to RESERVE (up) a few times to see if fuel flows in any of those positions. It should NOT from a properly functioning petcock.
 
#5 ·
I did last night. I disconnected it last night and hooked a longer piece of tube to the vacuum line and created my own vacuum using my mouth. I heard the diaphram pop. No fuel in the line or my mouth. I am wondering if it is happening while I am riding.
 
#6 ·
No I don't think it could happen while the engine is running. If the float is stuck open in the carb two thinks might happen, the engine get flooded by the excess fuel and quits and/or the fuel starts coming out the vent tube at the carb.

If the fuel was getting into the vacuum line while the engine was running, it would tend to flood the engine and I think it would quit.

The the fuel tank vent hose for kinks or blockage. It connects to the tank at the right rear.
 
#7 ·
The top of the tank vent tube did have a tear on it where it connects to the tank. I cut the torn part off and reconnected it to the tank. I did this before I noticed fuel in the motor for the second time. Thanks for you help by the way :mosh:.
 
#8 ·
That vent line should have an open Tee fitting about mid-point in its length and the other end is open to the ground underneath the bike.

I never heard of an issue like this caused by the vent line. Normally when it fails the tank doesn't let the fuel flow properly when the engine is running and you have a stalling lack of fuel issue.

But it doesn't hurt to check and see if each line is proper connected to where it should be. :)
 
#9 ·
I will have to check the vacuum line after work. I am beginning to wonder if there is some crud built up in the carb that is preventing the needle from doing its job correctly. There is some corrosion inside the tank. The previous owner did not do a goof job of taking care of the bike. I had part of the carb apart to check the float but did not check the needle. Odd thing is that when I ran the bike after changing the oil the first time is that the bike actually ran very well. I am aware of the dangers this causes. Luckily the gas did not destroy the clutch.
 
#10 ·
If the float is sticking and allowing fuel into the airbox, the crankcase vent tube can and will suck gas into the crankcase...Meaning it will happen while riding the bike.....I vaguely remember somebody within the last two months having that happen to them here on the forum.....:hmm2:
 
#12 ·
Got the carb off tonight. All seems fine. Float valve is ok. To my surprise the carb was very clean. Vacuum lines were all clear. I am beginning to wonder if the crud on the petcock was the culprit. It looked like seafoam was caked on the diaphram. As far as getting some gas back the second time when I changed the oil, I am wondering in there was still some fuel in the top end that hadn't made its way out. Won't be able to get the bike back together for a day or too. We'll see how she does. Thanks again for the help.
 
#13 ·
Problem Solved (I think)

Finally got the bike back together. Based on everything I looked at, I am going to conclude that the amount of corrosion on the petcock was the problem. As mentioned, it was cleaned and now functions properly. Lesson learned: shut the fuel off when not in use. Had the bike out last night and she ran good.
 
#16 ·
I made sure I checked for that when I took it apart. The petcock works as it should. Now I am running around the garage freaking out and disconnecting the fuel lines on my g/f's bike and my 4 wheeler. Probably taking it a bit overboard, but after what happened to my X, I don't want to take any chances. Not a very good feeling seeing gas pouring out of a place it shouldn't be. The X has sat for a couple of days now and has the same amount of fuel in it. With my luck, I am surprised the gas tank did not fill up with oil. I think that would leave everyone scratching their heads, haha. Thanks again to everyone for your help. :cheers:
 
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