Gas in air cleaners

Am I on the right page here guys? I am finding a very small puddle of gas on the floor under my bike. If I trace it back I find a drip from the air filter on the riders left. My thoughts are the float is sticking or the needle is worn down allowing gas to flow. It could be either side because the bike leans to the left when parked. Am I better off putting in a quick in-line fuel shut off or taking the time to rebuild carb. On a side note Im also sure gas is leaking into my oil and that needs to be changed before turning over again.

Sounds like a carb rebuild is in order. What model bike do you have and we need pics A nice write up of the bike would also be good cus we like stories too Welcome!

If we haven't seen pictures, it doesn't exist.

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Not neccesarly PC,anyone can post a pic and say this is my bike

Its a Yamaha XS400 Special. First time posting and I seem to be having trouble with pics. When I try and add one to reply I'm getting the error that I have entered to many characters, thoughts?

If you have a stock vacuum petcock it might be time to rebuild it because it shouldn't be allowing gas to flow without the bike running in the ON position, if you leave it in PRI then, um don't lol make sure its left in the OFF or ON position and if it still leaks in ON your vacuum seal is leaking...

Either way you have a carb issue, the petcock shouldn't be allowing gas to the carbs when the bike is off, and the carbs shouldn't be allowing the gas to overflow.

Recreateme said:

If you have a stock vacuum petcock it might be time to rebuild it because it shouldn't be allowing gas to flow without the bike running in the ON position, if you leave it in PRI then, um don't lol make sure its left in the OFF or ON position and if it still leaks in ON your vacuum seal is leaking...

Click to expand...

On my 82 I had the same problem and turned out to be a SLOW drip from the petcock when set on ON. I had a spare petcock which fixed the problem.

To check this before you start pulling the carb's, Leave the petcock set to ON.

1) Leave the bike on the side stand and pull the airbox cover and air filter. You should be able to use a flash light to look into the boot's and see some gas coming into the air box or at least smell it.

2) Remove the hose from the carb side. Hold a glass jar under the line and tap the line. You might get a bit of gas but at some point it should stop. If you get ANY slow drip's it will flood the carb's and cause to flow into the aribox. You can confirm by trying this by this on RES but regardless of on ON or RES there should be NO drip's. On PRI the gas will flow freely.

3) If it's not the petcock then it may be sticking floats. Regardless once you fix, replace the air filter and I would do a full oil and filter change ASAP in case fuel leaked back down the breather tube into your engine.

good luck

I feel that if the float needles are seating/floats set properly the bike shouldnt leak even when the petcock is on prime. I have left my bike on prime overnight with no leaking. Take your carb bowls off and then pull the pin holding the float in. Check the seat of the float needles. Its either got crud stuck in it or its gone to crap. Id replace them even if they "look" fine. They are cheap and gas ruining your cam/mains is not!

Hey all, came here to post about the same and saw this thread ... I've had trouble over past years with gas in my 1978 XS400 engine and always try to clean the carbs to no avail and have to replace my oil everytime i suspect it which costs me money (when i see some in the air cleaners). Pretty frustrating every year. This time i had emptied the oil yesterday. and left the engine oil plug out... and came today to see gas coming out of bottom of engine and the air cleaner .

1. I heard the float height has to be set correctly in this situation ...
I set it to 26mm (which is what most recommend since Haynes if wrong) but... is it 26mm from where the carb gasket would sit on the edge touching the bowl...
or slightly lower, on the inside of the carb? I read a thread here where said the inside, so i use that. Is that correct?

2. i adjust the metal tang in the middle of the brass float so that it gets me 26mm... but Im never sure about that 'outside tang' on the float. Imagine putting the carb upside down and pressing the float down... then you let go so it is flush just touching the pin. I adjust the outside tang so it can't really go much further (maybe just enough for a smalll separation between the pin touching the float). Is this correct or should you give it much more leeway so when it is sitting down it can rest further away from pin (because of gravity).
Here is the part of the vid where he mentions how this tang is important:

3. How can you tell if your float has a hole in it. I onetime saw my friends and it was pretty obvious it had a hole... but what about a slight hole in it, which would have only a little bit of gas in it. Just put it in water and see if it sinks?

4. Going to rest my tank to the side and see if it leaks out of the petcock (but i doubt it. Its a manual petcock thats actually pretty solid every year when Ive had these issues).

Note: have an inline gas filter so nothing should be clogging the carb. looks pretty clean in there.

Anyhoo, I'm really interested in Question #2 (outside float tang) as the rest is mostly just for my reference later on things to double-check .

The float is not a fuel shut off. If it was they wouldn't put in a petcock.
The float is a metering device. It controls the level of fuel in the float bowls to control air fuel mix. If the level is too high the bike runs rich, If too low the bike runs lean.
Leo

Leo the float is in fact a fuel shut off. The petcock's ability to shut off the fuel flow is actually obsolete on these bikes, but it's sort of an extra safety. The petcock is also either fully on or fully off, there's no real middle ground (unless it's leaky) which would make it impossible to regulate fuel flow to the carbs. You are correct that it also controls the level, but it also controls the shut off. If your floats are working correctly, you can run the petcock on PRI all day long without any trouble.

They may shut of the fuel flow under ideal conditions but that's not what they are designed for, the petcock is designed for that.
If I let the bike set in the sunshine with the fuel on prime The sun warms the fuel and air in the tank. Just this much extra pressure in the tank will over power the float valve and cause fuel to over flow the carbs.
This can't happen in the on position, as fuel only flows when there is vacuum applied to the petcock.
Leo

Btw, i may have found my issue. It wasnt even the float height possibly... My tank when i took it off to inspect the carbs more started to leak. so the manual petcock of the fiberglass tank stopped working optimally. and that leak into the carbs gradually flooded the bike.