Oil spilling out back of carburetors?? Help!

[jonny five]

Anybody have any ideas??

My bike is a 1981 GS750. I have noticed that, upon opening up the throttle even slightly or having the bike choked, I will eventually hear a slight air "pop/leak". I have traced this to the vacuum port on the second carburetor. Apparently the prior owner of my bike installed an aftermarket petcock which is not vacuum fed as there is no available port on the petcock, and thus the port on the carbs is left open. I have ordered a new OEM petcock, but am not sure if this will resolve the issue.

I removed the seat and the air filter as the oil is pouring out of my blowby box, and observed the carburetors as I held the throttle open to about 2500 rpm's. After about 10 seconds I heard the pop of air again, which was actually out of the back of the carbs, and the oil then starting pouring out!! I mean, gushing.

I've really gotten into working on my bike lately and am loving learning about it, but right now I'm not sure where to start tinkering. I feel like a knowledgeable mechanic could recognize what this issue is based off of these observations. So, any ideas??? I really appreciate the help!

 

[resjudicata]

Is the oil coming out of the mouth of the carb or out of the air box?

If it is coming out of the air box then it is being pushed out of the crankcase breather at the top of the valve cover, through the breather hose and into the air box.

If it is coming out of the carb mouth then I don't know what to say. I can't think of any way for that to be possible.

Chris

 

[jonny five]

It's hard to tell for sure, because the only way to see is by looking in the back of the airbox, and the oil really starts splashing out everywhere. It seems like a lot of oil to be coming out of just the breather tube, and since it is accompanied immediately prior by the pop of air out the back of the carb, I figured it was spilling out from there...also when I rev the engine I can see in my oil sight level that the oil bubbles violently, but maybe that's normal.

 

[Don-lo]

I would guess that the petcock has probably been left on, and gas has mixed with the oil. That mixture vaporizes and and vents into the airbox, looking like oil. This also explains what you see in the oil sight glass.

 

[Bill Alexander]

I would guess that the petcock has probably been left on, and gas has mixed with the oil. That mixture vaporizes and and vents into the airbox, looking like oil. This also explains what you see in the oil sight glass.

If there is enough gas got into the oil then the engine is going to be over full and oil (plus gas mix) is going to be pumped out the breather. First thing is to check your oil level.

You are probably also going to find that if the vacuum hose from the petcock is not connected to anything the carbs are going to suck extra air which may be the cause of the coughing back through the carbs.

 

[almarconi]

Do not run the engine with the port on the #2 carb open. You could put a hole in the piston due to a lean condition. This port should be capped if there is no hose attached to the vacuum port on the petcock.

 

[BassCliff]

Hi,

I concur. Cap the vacuum line to carb #2 if it is not connected to the petcock. Check the oil level. It is probably overfull because gasoline has leaked into the crankcase and diluted the oil. If there is gas in the oil, change it right now, do not run the engine until it is changed. Then I would change the oil again after about 500 miles or less. Getting an OEM petcock is probably a good idea but aftermarket "on/off" petcocks work fine too. Just remember to ALWAYS turn them OFF when your turn off the engine.


Thank you for your indulgence,

BassCliff

 

[jonny five]

Huh. Wow thanks for all the replies. I'll run a quick test, cap the port and see if that solves the air issue. Also I had suspected through reading other threads that maybe gas had entered my crankcase, but found it hard to believe that this could be the sole culprit of the massive amounts of fluid spilling out. I can't tell where my oil level is even tipping the bike back and forth, but I can just see the level when I look in with the cap off. This is all great info thanks again!!

 

[resjudicata]

If you can see the oil level through the filler opening and/or can see it in the sight glass while the engine is running then your oil level is VERY HIGH!! When you start the motor and the oil pump is moving oil through the engine the oil level in the sight glass should disappear while the bike is vertical.

Leaving the petcock on while the engine is not running is likely the reason you have gas in your oil. An EXTREMELY HIGH oil level is likely the reason you have oil/gas pouring out of your breather tube into your air box.

Chris

 

[tkent02]

The oil should be visible in the sight glass when it's not running, on the centerstand or balanced vertically on the wheels, and no higher than the window. If it's higher, lean it over to the left to see how much higher, you should take some oil out. If it smells like gasoline, drain it all and replace it.

 

[cyclefvr2]

Huh. Wow thanks for all the replies. I'll run a quick test, cap the port and see if that solves the air issue. Also I had suspected through reading other threads that maybe gas had entered my crankcase, but found it hard to believe that this could be the sole culprit of the massive amounts of fluid spilling out. I can't tell where my oil level is even tipping the bike back and forth, but I can just see the level when I look in with the cap off. This is all great info thanks again!!

its prolly over full, drain some into a container,and watch the oil through the glass , maybe just loosen the drain bolt ,while its still in there a lil will drain out, you can se the level go down, im betting its over full with fuel ?, i had this happen before on a older bike

 

[Steve]

Now let's go a step further to explain why the oil has had gas added to it.

Since you say that the petcock has been replaced with a manual unit (no vacuum fitting), I am going to guess that maybe you have not been turning the petcock to OFF when you stop the bike? The floats in the carbs can sometimes hold back the gas, but that's not their main job. They are designed to maintain a proper level in the float bowl, not hold back constant pressure of gas in a full tank.

Nice to see that you have ordered an OEM petcock, but if you change the oil and get the bike ready to run before it gets in, feel free to ride, just be sure to turn the petcock OFF when you are done.

.