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Fuel Leaking from the air box after warm up

  • Thread starter Thread starter Anonymous
  • Start date Start date
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Anonymous

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I have an 83 gs750ED with 33200 miles. the bike was in pieces when I got it. It had been in storage for several years. I went throught the carbs and got the bike running, runs good and pulls hard. Problem is that it leaks a small amount of fuel out of the airbox, obviously it is coming from the exhaust vent on the top of the engine.

1)I know that the petcock needs rebuilt.

2) I also changed the oil and filter.. would too much oil cause this???

3)I have also adjusted the float levels in .5mm increments from 19.5mm up to 23.5mm, the drip occurs at all settings. I resett them to the factory suggested setting of 22.4mm and get good low mid and high range engine response but can't get rid of the fuel drip.

I am out of ideas.

Would a bad petcock cause this???
Would too much oil cause this???

I am looking for any suggestions from the experts. I don't know if I can handle pulling the carbs off again... I don't have much skin left on the back of my hand from working on the engine while warm :twisted:

Help!!!!!
 
If there is fuel in the air box I would suspect that you still have a carb not working properly. Try running the bike without the air box so that you can see where the fuel is coming from. Did you replace the O rings on the needle seat assembly?? Also if it is leaking from the #2 carb it could be that it is sucking fuel from the vacuum line to the petcock.
 
Yeah. I would bank on a sticky float or improper needle height.

Too much fuel feeding into the carb. Also the #2 o-ring or petcock are also good suspects.
 
I appreciate the input, however there is fuel coming out of the engine exhaust port on the top of the head not directly from the carbs to the airbox.

If I pull the hose off the top of the airbox it drips fuel coming out of the head...

Thanks for the help and info..
 
Fuel in the head is not a good thing.
Fuel in the oil is a very volitile mixture.
When you changed the oil...did you see fuel in it ??
 
Fuel in the airbox can be spitting back thru the carb. This is common with a faulty or mal adjusted carb.
Run the bike without the filter element and inspect where the fuel is coming from.
Fuel in the head is an entirely different (serious) matter.

Be sure !!
 
yes when I changed the oil after the bike had sat for a long time there was fuel in the oil. I changed the oil and filter. Then rebuilt the carbs. I have not seen any fuel coming out of the carbs without the airbox on. I only see fuel with what looks like a small amount of oil in it coming out of the exhaust port on the head.. what does this mean???
 
What it means is that fuel is getting passed your combustion chamber and/or valve seals.
Have you done a compression check ??
This will give you an idea of the condition of your piston rings and valve seals.

Note: The wet stuff you see coming out of your head exhaust port might be water vapor/moiture. Does it absolutely smell like gas ??
Double check this.
 
First REBUILD the petcock. It may have flooded the crankcase with fuel again. Double check the oil for fuel. If there is any question about the condition of the oil Change it again. How much fuel is comming out of the breather hose?? drops?? or cup or two??? It could be that the first change did not get all of the fuel out of the engine.
 
There are other posts here that had similar problem.
Check these out for some more insight aswell.
 
i am waiting on the rebuild kit for the petcock. currently not riding...

it is gas with a slight mix of oil, for sure.. and it doesn't start until the bike warms up, and then it is just a constant drip at high rpms then goes away after a few minutes of idle. I know the petcock is bad. it never shuts of, I am currently using a clamp to stop fuel flow..

as far as a compression check, I don't have the tools... but when running and riding it feels like its all there.....
 
I bought a new GS750ES in 1983 and within a year the petcock leaked resulting in a crankcase full of gas. When this happens the rise in pressure can blow oil out the vent and even cause engine gaskets to leak. I also understand it's possible to bend a connecting rod during start up. Check that petcock.
Axel
 
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