Source of Gas leak to airbox

[moonstoner]

Ok, I found the "place" where gas is leaking out of the carbs and into the airbox (now only when the bike is running after I replaced the petcock with a new one). 1981 GS650G. It's emminating out of the two holes on the airbox side of the carb (I believe they are called the main air jet and the pilot air jet). Can somebody explain the plumbing of the carb to tell me why? I thought the floats were suppose to stop the flow of gas when full.
Thank you in advance.

 

[Guest]

Your float needles might be sticking , or they might be worn out not allowing them to close right.

 

[Nessism]

Float needles are not sealing. Time for a full carb clean up, replacement of the o-rings, intake boot O-rings if your bike has them, and check your gas tank for rust since particules will hold the float needles open.

http://www.thegsresources.com/gs_carbrebuild.htm

http://cycleorings.com/

 

[BassCliff]

Hi,

Here is some related material posted in another thread. I think this is from that GS guru, Mr. bwringer.

***********************

Let me point out the obvious: If a carb (or carbs) are overflowing when the bike is not running, you have TWO problems. First, your petcock should prevent ANY flow; second, the needle valve should allow flow only up to a fixed height in the bowl (ie, not overflow). Excess fuel has to make its way past both of these parts.

(A third possibility on old carbs is for fuel to flow past the inlet seat O-ring. [n/a for VM]. That doesn't apply to newly rebuilt carbs, since the owner has just installed brand new. Right??)

I'm not 100% sure why some needle valves leak and others don't, but I'm starting to lean with Keith Kraus' suggestion, which is to use only OEM valves and seats. Simply because it works. The question why is a separate matter. (I have a theory, but no guinea pig to test it on at present).

For the petcock, you'll hear a number of suggestions. I think that the vacuum operated petcock should be kept operational, for a few safety reasons.

Several of the folks here are convinced that petcock rebuild kits are useless, and your only real option is to buy a new OEM petcock.

For now, for people who are 100% sick of carb overflow & the ensuing problems, the consensus then is to go with OEM petcock, seats & needles. it's expensive, but it seems to be the only certain way to correct this BS once and for all.

(I would add: no doubt there are people whose overflow problems began when they installed carb rebuild kit(s). The machining on the parts is often abhorrent and inexcusably amateurish, and the f&^%#ing O-rings don't fit correctly. The consensus for a while now has been to buy gaskets IF you need them, valve seats & needles IF you need them, and an O-ring kit.)


The petcock does not, in any way, REGULATE the rate of flow. It should be either on or off. If you have overflow on a running bike (and it's not inhaling fuel through the petcock diaphragm via the petcock vacuum line) then there's a problem with the inlet valve.

Either:

1) the float is no longer buoyant enough or is badly adjusted, or

2)the valve is bad, or is being held open by some foreign matter.

And finally is the standard BWRINGER's lecture:

One of the secrets of the GS850 engine and carburetion is its outstanding low-speed manners. This, in turn, allows you to much more easily exploit the corners of its handling envelope, which leads to more giddy fun than you've ever had with your clothes on. As most racers eventually find out, smooth is fast.

If you had a freer-flowing aftermarket exhaust, a good set of K&N pods, a dynamometer, exhaust gas analyzers, a degree in chemical engineering, no neighbors to bother, a few weeks off work, a large box of Keihin jets, and several fifths of good tequila so you can sleep at night, you might be able to extract a few more horsepower from the 850 engine at certain RPM. And if you're really good, you might be able to get the low end half as smooth as it was stock. Maybe.

With the stock exhaust, forget it -- all you're going to do is screw up everything else quite badly to get maybe 5 more horsepower at 7,500 rpm or something like that. These things have a certain balance, and more intake flow must be balanced by more exhaust flow.


What I have noticed at the rallies is that very, very few 850Gs are actually running right. Make VERY sure it's actually running the way it's supposed to before busting out the modifications.

Brian's EZ-and fun plan for GS850 happiness:

1) Seal the airbox and air filter with weatherstripping.

2) Ensure no intake leaks. Spraying WD-40 or water doesn't tell you much, since very small air leaks can cause problems even though they won't suck in enough WD-40 to make a difference. Replace your intake boot o-rings and boots if needed, and seriously consider spending the lousy $28 for new airbox/carb boots.

3) Ensure clean carbs with correct settings, new o-rings, and original OEM jets. No, not just squirted with something. I mean completely disassembled.

4) Check/adjust valve clearances (Manual calls for every 4,000 miles. This is not optional.)

5) Ensure healthy electrical system.

6) Seriously consider upgrading coils and plug wires.

7) Install new, stock NGK B8-ES plugs gapped to .031".

8 ) Fine-tune float height and idle mixture screw to ensure best off-idle transition.

9) Clean air filter and reinstall with only the lightest oil mist -- over-oiling and/or letting the filter get dirty is a common and critical mistake, and will make the bike run funny at low speeds and run rich. This may take a few tries.

10) Make sure the exhaust seals are sealing.

11) Ooh, much better now, huh? You're gonna need upgraded suspension - Progressive or better fork springs and shocks. Set suspension sag appropriately.

12) Upgrade brakes with new pads and stainless lines to deal with all that extra speed.

13) Install new petcock, since I'm going to head to the roof with a rifle if I have to read about yet another #2 plug fouling and failed hillbilly attempts to rebuild the petcock and/or deny there's a problem.

14) Oh yeah -- check compression somewhere in there to ensure the valves and rings are reasonably healthy.

15) You'll probably need new OEM clutch springs -- the clutches last forever, but the springs get tired after 20 years or so under pressure. E-Z and cheap.
**************************

Thank you for your indulgence,

BassCliff

 

[saltykunk80]

mine was leaking same and was a stuck float on that particular carb

 

[dzane]

fuel leaking

fuel leaking

My 1980 GS 550 has a brand new vacuum petcock on the tank that just started leaking. I am with BassCliff on this, that the petcock should not allow ANY fuel to pass unless the engine is running, but alas, mine is. Brand new part. Brand new leak. So what to do about it? Is there something that can be done about the petcock? I am fairly tired of my shop smelling like it has been dipped in gas.