Gas filling the crankcase..

[Moody]

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

[steve murdoch]

Could be a stuck float needle.
There might be a carb clean in your near future.

http://zeus.mtsac.edu/~cliff/storage/gs/Mikuni_BS-CV_Carburetor_Rebuild_Tutorial.pdf

Welcome to the site.

[Hinermad]

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.

[tom203]

Test for correct operation with this new petcock- might be defective

[JJ]

Sounds like the float needle isn't holding.

[MadEyeGuy]

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.

[Guest]

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.

[MadEyeGuy]

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.

[tom203]

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.

[JTGS850GL]

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.

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.

[hillsy]

Check your bowl gaskets aren't interfering with the float and keeping it open - some aftermarket gaskets have been known to do this.

[limeex2]

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

[wymple]

If his petcock is working properly there wouldn't be any fuel dropping to get past faulty float needles. Fix the petcock.

[hillsy]

If his petcock is working properly there wouldn't be any fuel dropping to get past faulty float needles. Fix the petcock.

He says it's happening while its running.

[MadEyeGuy]

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.