Float not floating

[Guest]

Hi,

I have an 83 GS750ES with K&N Air filters and the Jet Kit. It runs really well except that the carbs will intermittently dump the gas in the tank into the crankcase when I forget to close the petcock. Over the previous weekend from Friday PM to Monday AM It drained the tank down to reserve. The float needles and seats are new. Yesterday while on the workbench hooked up to the auxiliary tank they didn't leak for 6 hours or so. Today two carbs began dripping after 3 hours. Theses are the original carbs and have never gotten a new set of floats. Can the floats absorb enough gas to the point they don't float well enough anymore.

Does anyone know a good way to test to see if the seat o-ring or washer are leaking?

THANKS!!!

[Steve]

If you have the stock petcock there is no way to "close the petcock".

Which position are you using to run the bike and which position are you using to "close" it?

Normally, you should run the bike with the lever pointing DOWN. When you start the bike, vacuum from the #2 carb will open the petcock and fuel will flow as necessary. When you stop the engine, a spring in the petcock will push a plunger back into place to stop fuel flow. If you go far enough to get to the REServe portion, turn the lever clockwise, so the lever is pointing FORWARD. This brings fuel into the petcock from a point lower in the tank, you have about one gallon of fuel left to find a fuel station. The last position is PRIme, with the lever pointing to the REAR. You should only need that to fill the float bowls if they are empty, like after a rebuild or if you have not ridden for a couple of months. It is NOT recommended to leave it in this position for more than the time it takes to fill the bowls, which is only a minute or so.

To test your petcock, use two longer pieces of hose. Connect one to the fuel outlet, the other to the vacuum port. Put each hose in a separate clear container and monitor them. There should not be ANY fuel coming from either hose, unless the petcock selector is on PRIme. Be careful with the containers you select. Clear soda bottles may not resist fuel. I have used glass canning jars, but you have to make sure they won't get kicked and broken.

You have plastic floats in your carbs. They don't absorb gas and I have not seen any of them leak. In order to have fuel leaking from the carbs, you have to have TWO failures: the petcock has to leak and the carbs have to leak. Either one is possible, but both have to happen at the same time. If the petcock leaks and the carbs don't, you won't know the petcock is bad. If the carbs leak, but the petcock doesn't, you won't know the carbs are bad.

The most-likely cause in the petcock is the o-ring on the plunger that stops the gas flow. You can get a rebuild kit to TRY to fix it, but the success rate for rebuild kits is about 10-15%, so you would be better off getting a new petcock.

The most-likely cause in the carbs is the o-ring around the needle valve that controls fuel level in the bowls. They dry up and crack, allowing fuel past the needle valve, overflowing the carb.

Let us know which petcock lever positions you have been using, then run two hoses into containers and let us know the results.

.

[jsandidge]

Over the previous weekend from Friday PM to Monday AM It drained the tank down to reserve.

If it has been leaking that much, you probably have a crankcase full of gas mixed with your oil. You shouldn't run it until you're sure the oil isn't contaminated. Open the oil fill and give it a sniff. If it smells of gas you'll need to change the oil and fix the leak.

[bwringer]

I've actually encountered a couple of leaking plastic floats -- the ones I saw were chemically damaged, probably by some idiot with a spray can of carb cleaner, so they were able to absorb gas. So it can happen. And it's depressingly common to find the float height set incorrectly, or crappy imitation parts from a carb kit (NEVER waste your money on carb kits), etc.

That said, the stock needles and seats were never designed to hold back a tank of gas overnight -- that's why Suzuki installed a vacuum petcock. Even if they're in perfect condition, they WILL leak gas when the bike is sitting if the petcock isn't shut off. Just a wee teensy droplet at a time, but over a day or two, you'll have a problem. Shutting off the petcock when the engine is off is MANDATORY.

Your best option is to install a fresh OEM vacuum petcock and think about something else for the next 20 years or so. Automagic, and nothing to remember.

[Nessism]

Aftermarket float needles and seats are hit and miss as far as quality goes. Mostly miss. K&L float needles for example won't hold up the weight of the float so their fuel hold-back power is limited compared to the OEM Mikuni parts. It's always best to measure fuel level in the carbs, not just float height. It's the fuel level that's really important, not float height. Another possibility is that you have rust and debris in the tank which is sporadically fouling one or more of the float needle/seats. Lastly, it's possible that the petcock has failed and is now allowing fuel to back flow down the vacuum line and into the carbs that way. Good luck.