Fuel Issue

[valhallan]

my 81 400 special has been sitting for a couple of weeks while i waited for a chain puller to come in. put it on last night, went to start it up and got a flood of gas on the ground. it was coming out of the air filter chamber. i discovered i had let it sit on the kick stand with the fuel valve open. i took apart the air filter, drained it, blew air through it to get residue out, and put it all back together. problem is i'm still getting gas out of it, like its backing up from the carb into the air filter.

is it possible its as easy as something clogged? or is there a more serious issue here, like i think? i'm not a mechanic, but if you show me the book or explain the issue, i can usually fix it.

i've only had the bike a few months, there was a lot of rust in the tank and while i THINK i've taken care of it, its still a possibility that rust could be causing clogs somewhere ( i REALLY hope its that easy!)

[Pat Kelly]

Use the SEARCH button to find numerous threads on the subject.
Boils down to:
-petcock letting gas by. XS1100's have vacuum petcocks so they can leak. You said you left it open so I'm guessing it's manual.
-float valve in carb(s) not sealing allowing fuel to leak past and flood the floatbowl. This overflows into the airbox and/or the crankcase (contaminating the oil). Check your oil for gas in it.

[valhallan]

hmmm

the fuel had an oil quality to it, enough to make me actually have to check it to make sure it was gas. if it is an issue with the float valve, i'm guessing my options are 1) open, clean, re-assemble, pray or 2) rebuild kit, pray or 3) new carbs?

[xs650mike]

XS400 fuel leak...

2 things...vacuum petcock not shutting off and float needle valves leaking slightly. Petcock is easy. Mikes XS manual petcock replacement. Part # 20-0019 http://www.mikesxs.com/mikesxs-fuel_...ategory_id=4.1 I've got one on my XS400 and it fixes this problem. Just plug the vacuum barb on the carb holder. Mike sells a blind plug for this. The petcock comes with different barbs which allow it to be used in a variety of configurations. This petcock will fit both XS400 and XS650 Specials but unfortunately won't work on an XS11. The float needle problem may just be intermittant because of crud in the float bowls occasionally getting between the needles and seats. Pull the carbs and clean the float bowls. Helps to install and inline filter too to prevent future occurances.


Of course you'll need to remember to turn the petcock on before starting the bike and to turn it off when you park. I've got a little note taped to the top of the tank that says, "Turn the gas on stupid!"

[valhallan]

YEAH

i tend to forget to turn the petcock on or off, and the real probel is when i ride to work, my ride is so short, i can actually make it there with the valve off, and just using the gas already in the engine and in the line. problem is when i go to leave work and the system is dry... takes a few tries for the gas to get back to where it needs to be.

[Parr8hed]

LMAO!! I have done that plenty of times. I have more than once had to leave the petcocks on prime for a min. to fill the bowls and let me start the motor without cranking on the starter for 10 min.

[valhallan]

ok, update

i took apart the carbs tonight, cleaned them completely, although they looked fairly good to start with, and put them back on the bike. opened the petcock, no leak. cranked the bike up, and it ran for maybe 10 seconds, sputtered and died and fuel starts coming out of the air filter again. cleaned out the filter, hoping (but knowing better) that maybe that was gas left over from before, and cranked the bike up again, and again it ran for a few seconds, sputtered and died and the gas again came pouring out the filter. so... i'm thinking the problem is definitly the carbs, and is the a re-build or buy new part issue? i don't know what all a rebuild kit includes, but i don't remember seeing new floats in them.

[Parr8hed]

sounds like you need to check your float height and/or clean/replace your needle jets. I am having a brain fart, but i think that is what they are called. anyway they are right underneath the floats. take off the floats, take out the jets underneath them and clean/soak/or just replace those. check the screens on them too. put all back together and then ajust your float height and then report back if still having the same problem.

[e.z.nightrider]

First bike I owned that I got to ride ( the first I owned was a 75 Norton Comando With Seven Miles on It, long story, lived at home, mom said no bike, my things moved to back porch outside, you get the picture) was a '79 XS400 Special. It had a vaccumm controled petcock. Check the O-ring on the diaphram (on the back side of the petcock, make sure it's clean, no scratches or tears) and also the float needles.

[valhallan]

floats

when i took the carbs apart to clean, i did pay special attention to the floats. they move freely and the piston like piece attached (is that the float needle?) also moved freely. i'll take a look at the petcock. as it is, i cant use the standard position on the switch (assuming its clogged) and have to run with it in the reserve position.

what i don't understand though, is why would only leak like this when it runs, and not when its sitting? i would think that if the gas is just flowing out of the tank because of a problem with the petcock, wouldn't it flow all the time? (i'm an engineer, i have to know WHY it works, not just that it does, sorry)

[Parr8hed]

the float needles on an xs11 are screwed into the actual carb body under the float. I can not speak for the 400, never had one apart. on an 11 you have to take them out with a socket wrench. that is why i supect that you have a problem with it when it is running. also the float level could be letting too much gas into the bowls while it is running. that could also cause the problem. you may ask some of the carb gurus on the "members lounge", I am not sure how many actually read the "other bikes" threads. just post a note to direct them to this thread. TC in paticular is great with carbs as are many others.

[e.z.nightrider]

If it only runs on res. your petcock is dirty or pluged. The reason it only leaks with the bike running is vaccumm from the carbs (there should be vaccumm line from a carb boot to the back side of the petcock) holds the o-ring open which lets fuel flow to the carbs, when it isn't running There is no vaccumm to open the o-ring and a spring holds the o-ring shut so no fuel flows even with the petcock on. If it only leaks while running I would guess that the float hight is wrong, the float needles are dirty and hanging up, worn and needto be replaced, or the float needle seat is dirty.

Ed Z.

[valhallan]

thank you

for the explanation EZ. i love it when things make sense lol. i think i only have 2 questions left (on this topic anyway) 1) if i have to adjust the float needle to allow in less gas, do i adjust it to extend more, or to extend less? i would assume less, but you just never know for sure, and trial and error is getting real old. my other question is quasi- related, could this issue also cause the engine to race when i'm stoped at a light due to the engine getting to much fuel? when i first got the bike, the engine raced like crazy, like it never came down even when i was sitting still, i cleaned the carbs and the problem eased up a LOT, but has gradually been going back to that same state since then.

sigh, another night with my wife complaining my hands smell like gasoline.

[Pat Kelly]

If it is a brass float check that it dosen't have a hole in it. Shake it and listen for gas inside it. If it's the solid plastic-type float then nevermind

[prometheus578]

"ChooChoo Charlie was an engineer..." (commercial for GoodNPlenty candy)

I'm confused by some of the posts here; whether you have a vacuum petcock or not. Either way, your floats are not shutting off the fuel. With a vacuum petcock, that would answer why it doesn't flood when off, but floods when they get engine vacuum. problem is with the floats or needle and seat.
("But wait... there's more! If you call within the next thirty minues, you will receive free...) As an extra bonus, you may have clogged float bowl vents! Had a Triumph that only leaked when running. Was clogged vents, though the Triumph Tech Line guy couldn't explain to me why. As a junior engineer and general idiot, I figured it out fer meself.
Carb vent is to allow air to leave the carb as the float rises, taking up space in the upper chamber of the bowl. If the bowl is not vented, the air above the floats becomes trapped. As the floats rise, this trapped air builds up a slight pressure. This higher atmosphere becomes more dense. The delicate working status of the float's bouyancy changes... the float is no longer able to "float" upward into this denser air, hence, it doesn't reach the apex of it's travel and doesn't fully shut off the fuel flow. Carbs will not leak when off... but will now leak when running.

Not bad for someone that doesn't know what he's talking about!
Check your carb vents, but also bench test your carbs. Take the bowls off, flip them over, turn on the fuel, and see what happens. Check for holes/fuel in the floats, too. Submerge them, using pliers, into a pan of hot water. the air inside will expand... and if you see bubbles, then you've got holes. Floats with fuel in them, being heavier, obviously will not float properly.

and it ran for maybe 10 seconds, sputtered and died and fuel starts coming out of the air filter again.

Yup... too much fuel... flooding out the sparkplugs.

there was a lot of rust in the tank

Clean the tank again and install inline fuel filters. You may have a chunk of rust between the float needle and seat preventing it from sealing and shutting off the fuel.