carburetors leaking gas into air cleaners

[curraninc]

why is fuel leaking out from my air cleaners when bike is not running.
A full tank of gas emptied all over my garage floor
1978 xs650 special 11 bs38 carbs:

 

[Paulrxs650]

Either your float height is incorrect, or your floats are sticking.

Whip the carbs off, check the float operation, adjust as necessary

 

[jchrisk1]

If you have vacuum petcocks, and they are on prime, they will continually flow gas. Make sure they are in the on position.

 

[Reid]

mine did the same thing put new needle and seats in and havent had a leak since...from the carbs atleast

 

[curraninc]

I just purchased 2 new manual petcocks and both carb overhaul kits from mikes xs.
Hopefully this will do the trick.Thanks for replys,
curraninc!

 

[leggers]

it may very well be the push in o-ring on the needle seat.

If that is not sealing correctly it will overflow like a sieve.

 

[curraninc]

thanks leggers,
i will over haul both carbs.
I also just purchased 2 carb diaphrams and both carb holders from jbm industries that are aircraft rubber material and are compatible with ethanol gas.
I will reply with results when finished.

 

[grizld1]

1. BS38's don't have push-in float valve seats sealed by O-rings. They have thread-in seats sealed with fiber washers.
2. Check floats as well as float valves.
3. Petcocks from Mike's XS are very good. Mike's XS knock-off brass (float valves, jets, floats) is junk. You might get lucky, but don't be surprised if those new valves don't seal.

 

[wilbur60]

Interestingly enough, I have a similar problem. Both carbs were working fine, then I took them off and adjusted the float level to a higher setting which should make it leaner. When I put them back on both carbs leaked gas out the back. So I adjusted the carbs to the previous setting and then they leaked even more! I would consider the needle valve to be the problem if it was only one of the carbs leaking, but both working fine, both adjusted, then both leaking? Seems unlikely that both float needles would fail at the same time. Possibly I put the needles in backwards, since they can go in two different ways. Am getting ready to go out and check everything again. Any other ideas?
THese are B34's, original brass floats

 

[wilbur60]

Interestingly enough, I have a similar problem. Both carbs were working fine, then I took them off and adjusted the float level to a higher setting which should make it leaner. When I put them back on both carbs leaked gas out the back. So I adjusted the carbs to the previous setting and then they leaked even more! I would consider the needle valve to be the problem if it was only one of the carbs leaking, but both working fine, both adjusted, then both leaking? Seems unlikely that both float needles would fail at the same time. Possibly I put the needles in backwards, since they can go in two different ways. Am getting ready to go out and check everything again. Any other ideas?
THese are B34's, original brass floats

 

[wilbur60]

Sorry about the double messages previously.
The problem is fixed for now. I used the clear plastic tube method. That is fantastic! My floats were off on both carbs. Yet I was going by the settings in the manual. The clear plastic tube I used was a 5/16" OD. It just barely threaded into the drain plug hole. (Tight enough so it would not leak) Then it is just a matter of getting the gas in the tube to the right height. How simple and effective. Whoever came up with that idea should be knighted by the vatican.

 

[curraninc]

what is that method of calibrating the floats with clear tubing?

 

[wilbur60]

I just could not get the float levels correct by measuring them according to the specs. Then I tried this technique where
1. I took off the carbs
2. Set them up so they are level just like they would be on the bike.
3. take off one of the float bowl drain plugs
4. put a clear plastic hose tightly into the drain plug hole (size 5/16 fits very tight but it can be threaded on with force.)
5. run the clear plastic hose down a coupe of inches to avoid a pinched line then looped it up so the end was higher than the top of the carb.
6. Create a temporary fuel supply to feed the fuel intake line. I put a small funnel tightly on the end of the gas intake line. Then I poured fuel into the funnel slowly until the floats reached the top and stopped the incoming flow of fuel. If the floats do not shut off the fuel then gas will start coming out of the back of the carbs. Obviously your adj are off if that happens. Remember, lower float levels ( for example 22 mm in comparison to 24 means your floats are allowing more gas in at 22, not less. So 24 is leaner, 22 is richer)
7. Pour gas into the funnel and keep pouring until the fuel in the clear tube will not go any higher. Then you know your floats are shutting off the fuel to the carbs.
8. The fuel level in the clear plastic tube shows how high the fuel level is in the float bowl. From there I can tell which way I need to adjust the floats, up or down.
9. It still is kinda messy as the gas has to be emptied out of the carb each time an adjustment is made, and there usually are several adjustments for each carb.
When the fuel level in the clear plastic tubing is even with the bottom of the float bowl flange (where it joins with the top of the carb) you are in the ballpark. That is where I stopped and my bike runs perfectly.
You could try doing this while the carbs are on the bike but I wouldn't want to. Much easier to adjust if the carbs are off and easily accessible.
If the tube is leaking, a little leakage is ok ( a drip now and then) a stream is not ok. Get a different size tube. Some folks buy an extra set of float drain plugs, drill holes in them and put on a nipple to make a very tight fit. I did not have the time to order, so I just used the 5/16 tubing and forcefully screwed it in. It worked fine.

 

[curraninc]

THANKS FOR THE REPLY WILBUR60.
i WILL CONSIDER THIS METHOD WHEN FINISHED OVERHAULING BOTH CARBS.\
HOW DO YOU ADJUST THE FLOATS WITH THE CARB BOWLS INTACT.DO YOU HAVE TO DISASSEMBLE THEM EACH ADJUSTMENT?

 

[wilbur60]

10-4. You must take the bowl off each time. It is a little bit of a hassle, but there only 4 screws to fiddle with. You only want to do one carb at a time. It took me about a half hour total, then another 15-20 minutes to put them back on the bike. It was time well spent.
If you are still using the screw heads I would take those to the nearest trash can and drop them in it. Go to ace hardware or anywhere that has a good screw selection and pick up a set of M5- .80 thread by 16 mm long screws. Get the ones that have the hex head because, with the proper allen wrench you will will not ever have to worry about stripping them.

 

[curraninc]

thanks wilbur60.
good info.!!!

 

[Jonb]

Hello everyone, I'm new to the forum but have had my xs650 for about 4 yrs and have had a couple issues ever since I bought it, one of which I was a rectifier but thanks to help from the forum that one is a thing of the past. Now I'm having trouble with a leaky carb or is it the petcock or float adj. I'm going to start with the petcock and move on from there because as I understand it there should be no fuel coming from the tank in the " on and res" positions and mine leaks. If anyone has more info I could sure use some help

 

[jchrisk1]

Fuel will flow in both the on and reserve settings. Vacuum petcocks will flow in the prime position. But not the on position(except while running).
When is the last time you cleaned your carbs? Do you run fuel filters? What year and model of carbs do you have?
If it was me, I would take them off and clean them real good and check the float height. Might be something in the float valve. Might be a leaking needle jet o-ring.

 

[grizld1]

1. The NJ O-ring sits well above max fuel level. If fuel rises that high, it's due to a defective float valve.
2. The float valve is a fuel metering device and is not designed to be a positive shutoff. If fuel is overflowing the vents, start with the petcocks and work down to the float valves. Both items need to be right.

 

[Drew650]

Hey all, I just received "new" EX500 carbs they were completely cleaned with all new everything. I just received in the mail today. I put them on and fueled up and gas started pouring from the air filter. Assuming the needle seats and floats are good, would this only be because of the petcock? Or would it be both the petcock and the carb float valve?

It is a vaccum petcock on a 1980 xs650 with the EX500 carbs. The fuel leaked on all the settings:RES, PRIME, and, ON.

Oh, and also the bike is not yet running either. If that matters.

Thank you and have a happy 4th! Stay safe