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Gas filling the crankcase..

  • Thread starter Thread starter Moody
  • Start date Start date
M

Moody

Guest
Hello all,

First lets start with the bike. 1982 GS 750T with V&H megaphone and pods. I've owned the bike for 10 years or so. This year is the first I've had this problem.

The problem: The crankcase filled with gas and shoots out the breather hose on the top of the valve cover. This happened about 6 weeks ago for the first time. I researched on here what could be the issue and based on others with the same issue that the petcock was bad. The vacuum side drawing fuel from the tank to the vacuum port. So I decided rather than rebuild I bought a new eBay unit. Worked good and no issues. Drove the bike a dozen or so times over a few hundred miles. Then I start it yesterday and its shooting oil/gas out the breather tube again. Crankcase is full of gas and oil. Maybe a faulty petcock again? Any ideas folks?

I appreciate any input.

Thanks!
Moody
 
I had a similar problem with a Triumph. Bees were building a mud nest in the carb bowl vent tube, causing the needle valves to remain open and allowing the carbs to flood and overflow into the cylinders, crankcase, and even the airbox. (That's why I don't own a Triumph any more.)

Granted, the Triumph didn't have a vacuum operated petcock and I had forgotten to turn it off manually, but those bee nests really aggravated the problem.
 
I know I'm coming late to this, but found it looking into the same issue on my '80 GS850G. The crankcase got full of gas and it foamed up into the air box, All the carbs were recently rebuilt so I don't believe the chances of three of the four puking gas into the box was the result of stuck float bowls, but I will check those out. The gas starts pouring out of the top part of the air box where the breather hose goes in.
 
Your floats needle is stuck open. If you have the petcock in "prime" position that will exacerbate the issue. Carb needs to be addressed. Sounds like time for a good cleaning and sync. Your issue will dissappear once the float needle is working properly. And avoid using prime position unless you run the carbs completely dry.
 
Thanks much. I will pull the carbs yet again, check the floats, re-install them and do a synch. The tank petcock is new and seems to be functioning properly. I only used the "prime" position when I initially installed them after cleaning. With the petcock to "on" it still puked gas.
It's depressing because all I want to do is ride it. Just before the carb work it would pour gas into the air box on shut-down. Now it does it once it has started running, almost immediately after start up.
I guess next weekends agenda is set for me.
I'll keep you posted, and thanks again for the good counsel.
 
Who rebuilt your carbs? There is an o-ring on fuel needle seat- you need to make sure that it's doing its job. Take carbs off, recheck stuff,and before reinstalling ,hold carbs in correct orientation and supply fuel into fuel T using funnel or something and wait. The needle seats should be able to block fuel flow for at least 1/2 hour before you see overfilling.

"With the petcock to "on" it still puked gas."

Shouldn't puked gas at all if engine is not running. Check for correct petcock operation in all 3 positions and don't assume just cuz it is a new unit- there are bound to be defective units. I check my 5 year old petcock regularly.
 
MadEyeGuy said:
Thanks much. I will pull the carbs yet again, check the floats, re-install them and do a synch. The tank petcock is new and seems to be functioning properly. I only used the "prime" position when I initially installed them after cleaning. With the petcock to "on" it still puked gas.
It's depressing because all I want to do is ride it. Just before the carb work it would pour gas into the air box on shut-down. Now it does it once it has started running, almost immediately after start up.
I guess next weekends agenda is set for me.
I'll keep you posted, and thanks again for the good counsel.
Click to expand...

If it's puking fuel after startup but not with the engine off then, at least, you've fixed the petcock problem. Now it's time to fix the float valves. Either they're set to the wrong height or you have a sticking/leaking float valve. One thing I like to do after a rebuild is to invert the carbs and blow air into the fuel inlet. You should not be able to flow any air with then upside down. Turn them over and you should be able to blow air through them. I usually do it back and forth a couple times just to make sure the valves are working correctly.
 
Check your bowl gaskets aren't interfering with the float and keeping it open - some aftermarket gaskets have been known to do this.
 
Most carbs will hold fuel even when left in "on" position if they are set up properly and in good condition. I agree with most of the others, re-check your carbs
 
If his petcock is working properly there wouldn't be any fuel dropping to get past faulty float needles. Fix the petcock.
 
Pulled the carbs and everything seems okay. Floats seem to be working properly. Next step is to start pulling jets and checking o-rings and levels while the air filter is drying.
 
MadEyeGuy said:
Pulled the carbs and everything seems okay. Floats seem to be working properly. Next step is to start pulling jets and checking o-rings and levels while the air filter is drying.
Click to expand...

And how exactly do you know the floats are working ok? None of the jets have O-rings. The only O-ring that can cause gas to keep flowing is the one around the float seat. Unless you forgot to put them on all 4 seats it would not be dumping fuel from all the carbs. Put the carbs level on a bench (I use a large bench vise) and use an auxiliary fuel tank. Fill the carbs and see which carbs are leaking fuel. Focus on the float valves on those carbs.
 
I know this thread is kinda old but i had the same issue of gas in the crankcase. A few months ago a rebuilt the petcock but problem persisted. Going off of what the previous post stated, I took the carbs off and put in a vise on a level surface and supplied gas from an auxillary tank, after about 30 seconds the #4 carb (far left) started leaking. Turned out it was the rubber O ring that is around the housing for the float needle. Old one had shrunk from age and the new one created a much better seal. Put the carbs back on a level surface and supllied gas, no more problem, had to adjust the pilot screws a little after the adjustment and its never run better. Hope this helps someone, and thank you JTGS850GL!
 
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thewarthog said:
..., after about 30 seconds the #4 carb (far left) started leaking.
Click to expand...
OK, please make up my mind. :-k

Was it #4 carb or was it the one on the left? They are not the same carb. :-\\\

The carbs are numbered from left to right, AS YOU SIT ON THE BIKE.
#1 carb is under your clutch hand, #4 carb is under your throttle hand.

Numbering won't matter in this case, since you found the culprit and it's on one of the outside carbs. Where it WILL matter is if you say you have a problem with the vacuum port on your #3 carb. Only the earlier VM carbs have a vacuum port on #3, your '82 1100G has BS-series carbs with a vacuum port on #2.

.
 
#1 carb yea I had a brain fart when i typed that, vacuum port on #2 as you stated.
 
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Here?s a story about a gas filled motor that could?ve been really bad. A friend had a 71 Dodge Charger 383 with a Carter 4 barrel carb. Him and his friend had been cranking on this thing for 3 days no fire. He asked me to stop buy to take a look and in doing so I found a broken wire to the ballast resistor. After fixing that I noticed they had the fuel line run into the large vacuum port on the baseplate! I fixed that.All that cranking was running gas directly through the engine to the crankcase. Pulling the dipstick it smelled like gas. I said Well I?m outta here,drain the pan an refill with oil and let me know what happened. Found out later they had drained 5 gallons of gas/oil out of the block. It?s a wonder it didn?t hydro lock. Got it started clattered for a few minutes and ran. Buddy sez runs great never been so smooth. One backfire while trying to start it could have ruined his day.
 
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