Gas Flowing out of Crankcase Breather hose

[Guest]

So I recently purchased my first bike with carbs, a 1982 GS850G with 20k miles for $800. It'll run for 30 secs or so then gas will come flowing out of the hose and all over the engine and I'm not sure where to start with diagnosing. Seller said he rode it regularly for about 3 months and that it had only started doing this a day ago. Somehow gas is getting into the crankcase. I'm gonna drain the oil and replace it once I get it figured out and I know better than to let it run anymore with that much gas in the crankcase. Any help would be appreciated and I can provide more info if needed.

 

[rphillips]

Check your oil, the fuel has probably leaked through the carbs & petcock filling the crank case with fuel & oil mixture...The first thing to look at anyway.

 

[Guest]

Check your oil, the fuel has probably leaked through the carbs & petcock filling the crank case with fuel & oil mixture...The first thing to look at anyway.

I did check the oil cap which smelled BAD of gasoline and what was coming out of the hose was gas/oil mixture, forgot to mention. What would likely be causing the carbs do be doing this?

 

[fastbysuzuki]

Sounds like your petcock has failed or you have left the petcock on prime and the weight of fuel has overcome the float valves. Either way you need to sort out the problem and change the oil and maybe the filter before you run the engine

 

[Guest]

That's possible! Like I said, new to carbed bikes. I'll get the oil changed, get the tank and air box back on and see if that fixed it. Is there a good way to "flush" the gas out of the crankcase? I feel like just draining the oil and filling it back up wouldn't rid of all the gas.

 

[rphillips]

Just draining & re-filling with a new filter will be fine, but if you don't find & fix the problem the gas will still be constantly and gradually leaking into the oil. If you found you had left the petcock on PRI., like fast said, turning it to "ON" may take care of the problem.

 

[Guest]

I'll try that, I appreciate the help!

 

[trent]

Had that happen to me on my 1100.
Bad petcock, bought a new old stock from dealership, bout $75 back then, it didn't last very long and same thing,
got through via vacuum line into number two cylinder if I remember correctly with second petcock, so number two had a miss

Been awhile??

Some one told me the float needle still should have prevented fuel from getting into crankcase.
they suggested carbs needed work also, ?

I put petcock from jp cycle and never had a problem.......

 

[Gorminrider]

Had that happen to me on my 1100.
Bad petcock, bought a new old stock from dealership, bout $75 back then, it didn't last very long and same thing,
got through via vacuum line into number two cylinder if I remember correctly with second petcock, so number two had a miss

Been awhile??

Some one told me the float needle still should have prevented fuel from getting into crankcase.
they suggested carbs needed work also, ?

I put petcock from jp cycle and never had a problem.......

Yes, that's one way-bad float needles and their seats

There's two ways for fuel into the sump: overflow from bowls into engine and/or through the vacuum petcock's vacuum line into engine-ie the vacuum diaphragm of the petcock has failed. Naturally,the first of these assumes the carbs are tilted toward engine (as they often are on the centrestand) or it would drain into the airbox.

 

[rphillips]

Thanks Grom, I'd always thought you had to have both faulty pet cock and needle and seat for fuel to leak in oil. You're right, if it flows through the vacuum line, the needle and seat can't stop it.

 

[Gorminrider]

yes, and IMO float needles (or petcock) should hold back a FULL tank of fuel whether on Prime or not.... there's of course always the exception: say, a tank with no vent heating in a parking lot

 

[rphillips]

A pet cock on PRI won't hold anything back, It's not supposed to. That's what PRI means, fuel runs through to fill (prime) carb bowls. Very common for needle and seats to leak "a little". Back in the old days we always needed to turn fuel off when not riding, as the needle and seats wouldn't completely stop the fuel. They didn't leak (seep) bad enough that when the eng. was running the eng. was using the fuel faster than the needles were leaking, so it didn't affect the running. But when left sitting for a while the fuel could (would) gradually leak through the carbs.

 

[Guest]

I tested the petcock, little bit of suction on the vacuum hose allowed gas to come through the mainline as it should've but it seemed like a lot to me. My vacuum line is also dry and doesn't smell so I don't think the petcock is bad, its not coming through the vacuum hose at least. Although I could be entirely wrong.

I replaced the oil and tried to get it to start but it was running like garbage and a couple exhaust back fires, what little it did run it would rev up with a little bit of throttle but anymore than a quarter turn and it would start bogging down. My current and only real idea is that its running like that because I haven't put the airbox back on yet and I was still fiddling around and didn't want to have to take it back off but idk if it would have that big of an impact. Any ideas would be very helpful!

Although I just remembered I took all of the hosing off the petcock and no matter what position I put the petcock in gas would flow out of the main. It only stopped once I put it halfway between Res and On and has seemingly since stopped and only flowing with vacuum.

 

[rphillips]

With the pet cock set to "on" no gas should ever flow until vacuum applied.

 

[Guest]

I tested the petcock, little bit of suction on the vacuum hose allowed gas to come through the mainline as it should've but it seemed like a lot to me. My vacuum line is also dry and doesn't smell so I don't think the petcock is bad, its not coming through the vacuum hose at least. Although I could be entirely wrong.

I replaced the oil and tried to get it to start but it was running like garbage and a couple exhaust back fires, what little it did run it would rev up with a little bit of throttle but anymore than a quarter turn and it would start bogging down. My current and only real idea is that its running like that because I haven't put the airbox back on yet and I was still fiddling around and didn't want to have to take it back off but idk if it would have that big of an impact. Any ideas would be very helpful!

Although I just remembered I took all of the hosing off the petcock and no matter what position I put the petcock in gas would flow out of the main. It only stopped once I put it halfway between Res and On and has seemingly since stopped and only flowing with vacuum.

sounds like you have multiple problems.

1-the petcock is bad (unless you left it on PRI).

2-you may have a bad float and one of them may be stuck or bad and sank to the bottom of the bowl. causing a fuel leak.

3-float overflow vent is clogged.

on my bike, i had a float go bad. fuel would pour out of the carburetor vent hose. the same should happen with yours.

some time ago, i bought a set of needle valves and floats as a kit. the needle valves were a little too long and the anti-surge spring in the needle was stiffer than stock. the float adjustment tab angle had to be very steep to maintain proper fuel level. the steep angle of the float tab caused the float to be stuck in the down position. with that said, i suggest removing the carbs, check the floats and chase all the ports and vents with carb cleaner. hope that helps.

 

[Gorminrider]

I tested the petcock, little bit of suction on the vacuum hose allowed gas to come through the mainline as it should've but it seemed like a lot to me. My vacuum line is also dry and doesn't smell so I don't think the petcock is bad, its not coming through the vacuum hose at least. Although I could be entirely wrong

I don't think you are wrong. But it's important to know a full tank of gas exerts more pressure than a 1/4 full tank that the vacuum valve has to hold back....

But float needles should hold the fuel pressure back too,irrespective of the petcock.You can emulate this without "a full tank of gas"by raising a small tank(or a funnel) attached to the fuel line to the same level as the full tank's fuel level is on your bike .

Float needles and seats wear out. apart from gum/dirt, Look for any ridges or scratches or marks on the needle and it's seat.... "cleaning" with anything more than a cotton q-tip and some gasoline is a bad idea....people have tried to hone the seat with fine valve-grinding compound but I'm not telling you to do it-it's a desperate fix that can make it worse.