carb overflow mystery

[KEITH KRAUSE]

'79 GS1000L pods and straight pipe. The straight pipe isn't a quality pipe. It's not tuned in any way. Jetting problems right there. I know your engine and carbs well.
If the engine is tuned per the factory manual including valve clearances and ignition timing, you have good clean carburetion and you have good compression, then jetting is fairly easy with a QUALITY pipe.
130 Mikuni mains are the same size as Dynojet 138's which is what DJ supplies in their stage 3 jet kit. That main size is proven to run well with pipe/pods/w/w/o minor cam and bore increase. If you don't get the kit, run 130 Mikuni's.
Lower the e-clip on the jet needles to the bottom position and place an approx' .022" thick jetting spacer directly on top the e-clip. Then thicker stock plastic spacer on top the jetting spacer. Thinner stock plastic spacer under the e-clip. This equals position "4 1/2". Most common setting for good results.
Try the stock #15 pilot jet with richer pilot fuel screw adjustments up to 3 full turns out. If not rich enough, go to a 17.5 PJ and return the screws to approx' 3/4 turn out. As always, fine tuning needed for each cylinder.
REMOVE the 2 floatbowl vent lines. Leave the ports open.
As for your first post saying the carbs overflow as soon as you turn on the petcock, the float needle valves should stop all flow if they are in good condition and are the correct valves and are installed right side up. Also, the valves and seat wear as a unit, so they should be kept as a unit and never mixed with other valves/seats. If they don't stop flow, you have debris up inside the float valve seat, or worn valve tips, or a possible burr along the side(s) of the valve needle. If the valves check OK then your floats aren't operating correctly. That could be from a mistake made in height adjustment or their movement is hindered by being bent or even punctured. If fuel is flowing out of the lines attached to the bottom of the float bowls then the problem is something mentioned above.
Could be a dirty tank or even pieces of rubber breaking off from inside the petcock.

[KEITH KRAUSE]

One other thought, if you have aftermarket float needle valves, some brands are poor quality and leak upon initial installation.

[John Kat]

One other thought, if you have aftermarket float needle valves, some brands are poor quality and leak upon initial installation.

I recently changed my float needle valves on the VM 30's that come as OEM equipment on the GS 1000 ST's sold in Europe.
As the parts are obsolete, I had to use shortened BS 34 seats in conjunction with VM 26 needles.
To my great disappointment, two of the carbs are overflowing
I wonder if it's the same quality issue you are mentionning?
On the picture you can see the VM 30 next to the BS 34 needle valves.
Update: I started the engine again this morning and...no overflow anymore!
Big mistery!

[KEITH KRAUSE]

Aftermarket float needle valves are often inferior in both materials and their precision. Trying to make them work with existing seats often creates leaking. They're infamous for having weak springs too.
Hope yours stops leaking. Sometimes parking on the centerstand helps minimize leaking. A questionable operating float needle valve will sometimes seal well enough when basically straight but leak when on the sidestand. Can drive you nuts if you've done everything you can to fix the problem.
At that point all you can do to to counter overflowing when parked, especially when parked for longer periods, is to install a non-vacuum petcock such as a Pingel or a petcock with an "off" position, or install an inline on-off valve. When you're within say, 1/3 of a mile of your destination, turn off the fuel supply. The still running motor will generally use up most of the fuel still in the fuel line and carb passages leading to the bowls. The idea is, with little or no fuel in those passages, no fuel can get past a poor sealing valve and so no overflow or too-high float bowl fuel level at next start up.
Depending of course on throttle usage and motor rpm's, it takes anywhere from 1/3 to 2/3 of a mile before you can experience the first sign of fuel starvation after turning off the fuel supply. Obviously you have to be careful you don't compromise your safety in traffic near the end of a ride by allowing the carbs to get low in fuel. Most commutes you know what you can get away with if you decide to try this. Going 1/3 of a mile is generally safe and the carbs act as normal. After arrival you can also moderately rev the bike a minute or two and that will also use up the fuel. No need to run until stalled, just until obvious first signs appear.
Just an option if you're being forced to live with a "mystery problem" such as this.

[Steve]

At that point all you can do to to counter overflowing when parked, especially when parked for longer periods, is to install a non-vacuum petcock such as a Pingel or a petcock with an "off" position, or install an inline on-off valve. When you're within say, 1/3 of a mile of your destination, turn off the fuel supply. The still running motor will generally use up most of the fuel still in the fuel line and carb passages leading to the bowls. The idea is, with little or no fuel in those passages, no fuel can get past a poor sealing valve and so no overflow or too-high float bowl fuel level at next start up.

Just trying to wrap my little mind around this concept.

If you install a manual petcock or an on/off valve, why do you have to run the gas out of the bowls?

Seems to me that if you POSITIVELY have the gas shut off with your manual petcock, nothing is going to leak anyway.

Or am I missing something here?

.

[KEITH KRAUSE]

After shutting of the fuel supply there's still fuel in the line and fuel passages to each carb float chamber. There's enough fuel to easily overflow one or more bowls if the valves don't seal as they should.
You would like to think that there's a positive seal via suction from a closed off fuel tank (no venting). Like a straw, dip it into water, cover the top with your thumb and the straw shouldn't leak. But take the straw and rotate it at an angle and the water drains quickly.
Because our fuel lines are bent at an angle and are not a straight enough drop below the tank, fuel can flow. Generally much slower but it does flow. That's important if the bike sits overnight or longer. Gradual dripping will get past the poor sealing valve and overflow the bowl or at least allow a high bowl level that gas fouls the plug until the motor warms up well.
Common problem that many aren't aware of what's happening. What I said earlier is an option for someone who simply can't fix the leaking.

And I didn't say to run the gas out of the bowls. I said after shutting off the petcock to ride/run the bike long enough to use up the majority of fuel in the fuel line and carb passages to the float chambers. Hard to know exactly when that it so park and rev it some and soon you'll feel/hear the first sign of fuel in the bowls getting low and then you shut off. Do it a couple times and you'll know just what to do to use up enough fuel in the fuel line/carb passages to avoid overflowing. Generally, about 1/3 of a mile and another minute of idling/revving will do it. Or if it's safe, ride the last 2/3 mile and you'll hear the first sign. Whatever combo works best.

[wompin]

Its spring and i cant ride. HELP PLEASE!

So, its been a long while since Ive posted here, but Ive got some more issues with my bowls overflowing.

The float needles and seats are clean and there are no signs of wear.

When I isolate the petcock, It works properly and does not leak.

When I isolate the float valve assemblies, they hold back water.

When I test the carb bank off the bike, It does not overflow.

BUT, when everything is buttoned up back on the bike, it ****es gas onto the floor. What gives? (yes I do have the bike held upright and not on the side stand)

The only thing I can think of that is causing my overflow problem is that my floats are not fully closing the gas inlet valve (needle and seat). Mayble the floats are not as bouyant as they should be. They do float, but maybe not well enough.

Does anyone perhaps have a picture of how the floats should look while floating in water for comparison? Id rather be sure what parts are causing my problem before I just blindly replace everything (ie floats, float needle and seat, seat washer, petcock, etc)

[barnbiketom]

exactly WHERE does the gas come from/ if you need to, move the airbox back out of the way and tell me WHERE the gas is coming from

[chuck hahn]

Leaky fuel joints can weep and drops can form on the bottoms of the bowls..or actually some pretty staedy dripping if the orings are real bad.

[nejeff]

My son had a KZ400 that we could not get to stop leaking. The float valves appeared to be working correctly but finally decided to replace them and it stopped the leaking. Did not have time to re-read all of the thread but I would say that's a place to start.

Also if you have the on / reserve petcock I have on my 80 550e you can grind the stop nub off the bottom of metal bezel and rotate the petcock to that area opposite of reserve. This will be 100% positive stop of fuel

[Gorminrider]

wormpin, obvious first- you checked float level measurement of course...
something has to be wrong in your tests. A full air-vented tank of gas has pressure equaling sum of column height over float needle. so bench tests should/could involve just a long tube full of gasoline...
My question:why involve water for float test? you know water is much denser than gasoline and floats will be too buoyant -what help in deduction? (also, water "leaks" differently,especially when it's flushing surfaces covered with previous distillates)

I'd say, even Paint thinner or kerosene is better than water if your're worried about exploding hazard...?

[wompin]

exactly WHERE does the gas come from/ if you need to, move the airbox back out of the way and tell me WHERE the gas is coming from

Im not sure I know what youre asking, but the gas goes in the center inlet "T" on the carb bank, through the carb passages and past the gas inlet valve. This is where the leak is occurring. Then, obviously, my bowls fill to the height of the overflow pipe, and out the overflow tubes onto the floor. My guess is this is not what you are asking since this info is obvious

[wompin]

Leaky fuel joints can weep and drops can form on the bottoms of the bowls..or actually some pretty staedy dripping if the orings are real bad.

This is more than weeping. When the bike is running, and for several minutes after the motor stops, gas overflows out of the overflow tubes probably every 30 sec to 1 min. Thats more than just drips. My float height is not that far off either.

[wompin]

wormpin, obvious first- you checked float level measurement of course...
something has to be wrong in your tests. A full air-vented tank of gas has pressure equaling sum of column height over float needle. so bench tests should/could involve just a long tube full of gasoline...
My question:why involve water for float test? you know water is much denser than gasoline and floats will be too buoyant -what help in deduction? (also, water "leaks" differently,especially when it's flushing surfaces covered with previous distillates)

I'd say, even Paint thinner or kerosene is better than water if your're worried about exploding hazard...?

You make some good points. Im am thinking my bench test gave useless results since my fluid was water. I was just sick of smelling gas and I didnt think the different fluid properties would effect the test that much. I suppose in reality the lower specific weight (density) of gasoline will reduce the surface tension and gas could leak where water will not.

I think I will try purchasing new float needles and see if that solves my issue before I pull the carb bank out again for testing.

[wompin]

My son had a KZ400 that we could not get to stop leaking. The float valves appeared to be working correctly but finally decided to replace them and it stopped the leaking. Did not have time to re-read all of the thread but I would say that's a place to start.

Also if you have the on / reserve petcock I have on my 80 550e you can grind the stop nub off the bottom of metal bezel and rotate the petcock to that area opposite of reserve. This will be 100% positive stop of fuel

I will try buying new float valves. At this point I just want the problem solved. As far as my petcock, I have had a siphon test going overnight, and so far there is no leaking past the vacuum petcock diaphram while no vacuum is applied.

Test: tank sitting on stool, gas line runs down to clear jug, suck on vacuum line to get some flow, leave gas line end below surface. If there are pinholes in the diaphram or other leak problems, the siphon effect should slowly pull gas through the line. I marked initial gas level in the clear jug, and I have seen no change is the level since yesterday.