Vacuum tap + Carb seat leaks = Massive flooding - my 79SF

[steptoe]

its like most things on these bikes good and clean will do, but sometimes pedantically clean is needed,
the ceramic disc should be able to be sucked on but not blown into, if so it,s cactus

as for vents in fuel caps, most of the time I can hear mine wheezing when hot, so I know its good

[excess.11]

2 things interest me....first....the vacuum port check valve...ceramic disc to stop fuel getting up the vac line..
Did nt even know they were in there .
I d also be checking the vacuum hose and carb mount vac spigot that they are nt partially blocked and that the vac hose is not switched around with the vac timing unit spigot.
If the in tank filter is deformed or allowing unfiltered fuel from the tank to the seat......residue and rust etc could hold it open . So a clean tank is imperative as well as a well sealed and fitted in tank filter to the tap.
What about the tank cap vent hole and vent tube ....to allow pressure to stabilise in the tank .
When you stop your bike after a run ....the heat from the engine nicely warms up the tank and pressurises it.
This expanding air must be able to vent freely .
How often do we check venting though the filler cap or vent tube ?
Any pressure building in the tank may push the seat open.
I t s common point I hear when there s flooding ......comments are....it s fine when I m riding....but when I stop it starts flooding.

[excess.11]

I m a "Demon" for chasing down a problem .....there is reasoning for everything ...(except for what a woman s thinking) hahaha.
So........if everything is perfect as you ve described .....it should be working .....but.....here s the Clanger....it s not!! As you ve mentioned.
So....logically....you ve missed something or don t have something quite right....or the seat is damaged beyond repair.
Anyhoo.....it s your prerogative ...you can lead a horse to water...etc etc.
I ll go over the details and see if I can spot something you may of missed or could be an issue.....just for my own satisfaction.

[Jonesy :-)]

Yep, good tutorial, the guy pretty much copied what I did, even down to dremel polishing the seats. Not going to waste any more time and money on it, so the "mod" will do, for me anyhow.

[AussiXS11G]

get rid of em.......
install on/off/res taps

 

[excess.11]

Ok............here is the tutorial......it may show where you guys are not paying enough attention to detail in repairing these taps.
They DO work ...and work very well...........but like everything....they get old and tired and need some loving care.

http://xjbikes.com/forums/threads/rebuilding-the-yamaha-vacuum-fuel-valve-w-pics.25058/

http://www.xs650.com/forum/showthread.php?t=20662

[excess.11]

Thats what I m a sayin Jonesy........
As yet you have nt located the issue as to why it leaks. The tutorial I recall.......and wish I could find.......covers the issues you need to look for and how to repair them.
I ll keep looking.

[Jonesy :-)]

Hey Jeff,
I've tried to correct the leaking tap/carby problem the correct way, by throwing new parts and dollars at it only to find 3 days later a pool of fuel under the bike, so for me, it (the fuel tap off mod) was an almost fool proof way of fixing, never had a while you ride flooding problem, only ever while it was parked. Last time it leaked was at wellington this year and leaked overnight because I forgot to turn taps off. I have left it parked with taps on on other occasions and not leaked too?So I would recommend it as an almost fool proof solution. As long as the fool remembers to turn the taps off it'll work

[excess.11]

Why are you guys doing this so called mod?
Don t reply...I do know....but it seems the quick bandaid fix rather than find the issue and deal with it.
There is always the chance you may inadvertently forget to isolate the fuel.......and have to deal with this issue at a more inopportune time and place...... is all I m thinking.
I recall seeing a very well detailed blog/vid on what to look for when refurbing fuel taps and how to do it.
Hope someone will know the info blurb and recall where it is....it was a great detailed piece of info.

[steptoe]

you forgot to mention the air filter

[Eveready1100]

I'd decided that I'd get out and go for a bit of a ride last weekend, so I walked into the garage kitted up, and noticed a pretty strong smell of fuel. Had a quick look at the sightglass and saw it was full to the top (nothing unusual there, as it uses a bit of oil, I keep it to the upper edge of the window).
Thumbed the starter and the motor wound over, and over and over, which was unusual as it normally fires on the first RRR. Looked down to see fuel pouring out from under the airbox onto the cases. Hmmm, I took the bike off the centrestand and wheeled it outside so I wouldn't stink the house out with fumes. Kept trying to get it going, but it was being very stubborn this morning and fuel looked to still be pouring out of the airbox when I stopped cranking for a few seconds.
The I decided I'd remove the filter and have a look at what was going on while I cranked it over. For a few seconds there was nothing, then I stopped trying when I saw a gout of frothy muck spew out of each carb mouth and down onto the cases.
That made me think to investigate a bit deeper. It turns out that while the bike had been sitting, one fuel tap had been slowly leaking fuel into the carbs, one of which obliged by letting its float needle leak fuel into the motor which slowly filled up. When I was attempting to start the bike, the crank was thrashing the petroil mixture into a foamy mess which was then blown out the crankcase breather into the carb mouths which lubricated everything nicely.

I drained the sump this morning and relieved it of 11 litres of liquid (that's what was left in there) , moseyed on over to the Bundy Bike Hospital and borrowed another oil filter (last oil and filter change was 60klms ago!!!) buttoned eveything up, filled with more fresh oil, thumbed the starter and it went on the first RR, just like any other time.

I have a large industrial fan at one end of the garage which I turned on with the door open and let the bike run for some time to try to let the stuff in the pipes burn off. I haven't got it all out yet, so I think I'll find a deserted backroad in the vicinity to burn the rest of the oil out of the pipes. I don't was the mighty XS1100 be seen as a smoky old thing, do I?

Oh, I have also done the "fuel tap off position mod" now, so this shouldn't be an issue ever again.

Short vids below