Fuel leak when the engine is running only?

I can't see ST1100-Leak section (does it mean ST1100 should never leak?!? ) so I'm gonna post it here.
This morning while putting the gear on me I turn the bike on to "warm" it up a little bit. Put my cloths to bags, took the garbage bin to the street, went back home to say to my milady and the, when wanted to hop on the bike I found a big fuel leak under the bike. And still dripping. About a drop every sec or two. Turned it off, moved the bike to the driveway to clean the leak. After I finished I took a look at the bike no leak under it on driveway. I turned it on again and shortly after it started leaking again. I turned it off and it stopped leaking again.
So, any idea what ti could be? Or where to start?

Thanks,
Afan

The only way to find it will be to pull the plastic and inspect; so, I'd start there!

Really, you can guess it'll be the vacuum shutoff, if it is still there; but, it just as likely to be a cracked fuel filter or one of the fuel lines.

At least you can reproduce the problem!

Good luck,
Mark

At least you know the fuel pump is working! Time to take the clothes off for a look. Right and left side covers and top shelter, at minimum.

stuck float?

Since I'm really bad in fixing stuff (except if it's REALLY simple, like taking off the plastics - what I managed to screw up too by throwing all screws into the same can so god help me/us when the time comes to put it all back together ), I called a friend of mine - he's kind of car/moto mechanic, and he's almost sure it's one hose just under the carburetor. We couldn't take off the carburetor because I didn't have a right tool for it (all my screwdrivers are china-made and so easy to mess up the screw), he didn't had with him. So, he's coming tomorrow again.
Scary watching him taking off all those parts and looking at my bike naked. I REALLY hope he knows what is he doing

Afan said:

Since I'm really bad in fixing stuff (except if it's REALLY simple, like taking off the plastics - what I managed to screw up too by throwing all screws into the same can so god help me/us when the time comes to put it all back together ), I called a friend of mine - he's kind of car/moto mechanic, and he's almost sure it's one hose just under the carburetor. We couldn't take off the carburetor because I didn't have a right tool for it (all my screwdrivers are china-made and so easy to mess up the screw), he didn't had with him. So, he's coming tomorrow again.
Scary watching him taking off all those parts and looking at my bike naked. I REALLY hope he knows what is he doing

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OOOH BOY! I too hope he knows what he is doing. Do you at least have the Honda Service Manual there? It can help with carb disassembly and also help you figure out which fasteners go where on the plastic. All FOUR carburetors come out as a unit, but be sure to tell him NOT to remove the rubber snorkel assembly that sits atop the carbs. They don't need to come off to remove the carbs and are a real PITA to re-install, if you do. What year is your ST1100? You may need to replace the four carb "boots" that mount the carbs to the engine. They get old and brittle and you want to ensure a good seal when the carbs go back on. Good luck!

When taking off plastic, I always keep each set of fasteners with each piece of plastic as it comes off. Not hard to figure out where they go once it starts going back together.

Bush said:

OOOH BOY! I too hope he knows what he is doing.

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Me too...

Bush said:

Do you at least have the Honda Service Manual there?

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Yes.

Bush said:

All FOUR carburetors come out as a unit, but be sure to tell him NOT to remove the rubber snorkel assembly that sits atop the carbs. They don't need to come off to remove the carbs and are a real PITA to re-install, if you do.

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Bush said:

You may need to replace the four carb "boots" that mount the carbs to the engine. They get old and brittle and you want to ensure a good seal when the carbs go back on.

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I will, thanks a lot for the tip.

Bush said:

What year is your ST1100?

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1998

Bush said:

Good luck!

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Thanks, I'm gonna need it! :cry:

Bush said:

When taking off plastic, I always keep each set of fasteners with each piece of plastic as it comes off. Not hard to figure out where they go once it starts going back together.

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NOW I know too...

Bush said:

When taking off plastic, I always keep each set of fasteners with each piece of plastic as it comes off. Not hard to figure out where they go once it starts going back together.

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Sound advise
Didn't do that the first time I took the fairing off, and I ended up with some spare bolts on the floor ...

Woonjas said:

Didn't do that the first time I took the fairing off, and I ended up with some spare bolts on the floor ...

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Hm... Why I see that as "my" scenario too?!?

Bush said:

You may need to replace the four carb "boots" that mount the carbs to the engine. They get old and brittle and you want to ensure a good seal when the carbs go back on.

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With "boots" you were thinking on these 4 rubber "thingies"? They look in pretty good shape to me.

P.S. I didn't took the image, it's from the other post. (http://www.st-riders.net/index.php?topic=10249.0)

Afan said:

With "boots" you were thinking on these 4 rubber "thingies"? They look in pretty good shape to me.

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No, those are the intake "snorkels". The boots or "insulators" as they are properly known, connect the carbs to the engine.

Part # 16211-MT3-000 - $8.84 ea at Partzilla

Check that small, thin sub filter (foam piece) that is in the small box that connects to those two larger hoses going into the carb banks. If it is looking at all like it is coming apart, replace it, as bits can be sucked into the carbs causing more problems you don't want.

Just amended post #11

Bush said:

Just amended post #11

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Thanks.

Bush said:

No, those are the intake "snorkels". The boots or "insulators" as they are properly known, connect the carbs to the engine.

Part # 16211-MT3-000 - $8.84 ea at Partzilla

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+1!.......Do NOT even consider re-using the carb to head boots. A holed piston WILL ruin your day.

Bush said:

Just amended post #11

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What else would be good/wise to change at the time?

Afan said:

I'm sorry but don't get it...

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Irish is referring to the fuel shut off valve, actuated by engine vacuum. Located just above, and connected to, the fuel filter. There is a thin diaphragm in there that can tear over years of use, although, I'm not aware of that causing a fuel leak, more of a fuel starvation issue. That is, unless the vacuum hose connected to it can suck fuel through the open diaphragm? That item is usually bypassed when fuel starvation is an issue.

Afan said:

What else would be good/wise to change at the time?

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Well, we could open up a real can of worms there, having the carbs out, but I hope your friend is sure he really needs to pull the carbs to find the leak. Have you run the bike with all the bits off to see, or try to see, where the leak is?

Allow me to digress here a bit. Something I'm not clear on is whether all North American models have the PAIR system after the year 1996? Originally, I thought all post '95 models had PAIR, but my '96, just bought last summer, does not have it. The PAIR system is employed to reduce emissions and can easily be identified by four chromed tubes coming out of the cylinder heads by the exhaust pipes, visible through the side maintenance covers. Maybe only California models had it on later years??

Anyway, if you have that, you will find a mass of stuff buried under the carbs, but what you really want to take a good look at is the condition of the cooling system hoses, also found in that space. Your friend should be able to ascertain their condition and if they feel at all too soft or are swollen, they should be replaced, along with the smaller bypass hose contained in there as well. THEN . .. . if it is necessary to replace those hoses, you should also replace the "elbows" and the o-rings inside them, which mount the hoses to the head.

Have a good look in there first and report back, if your friend is unsure of anything in there.

Bush said:

Allow me to digress here a bit. Something I'm not clear on is whether all North American models have the PAIR system after the year 1996? Originally, I thought all post '95 models had PAIR, but my '96, just bought last summer, does not have it. The PAIR system is employed to reduce emissions and can easily be identified by four chromed tubes coming out of the cylinder heads by the exhaust pipes, visible through the side maintenance covers. Maybe only California models had it on later years??

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I would assume his bike would've had the PAIR system since my '98 did before I got a hold of it.

Bush said:

Irish is referring to the fuel shut off valve, actuated by engine vacuum. Located just above, and connected to, the fuel filter. There is a thin diaphragm in there that can tear over years of use, although, I'm not aware of that causing a fuel leak, more of a fuel starvation issue. That is, unless the vacuum hose connected to it can suck fuel through the open diaphragm? That item is usually bypassed when fuel starvation is an issue.

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Since the fuel leaks only when motorcycle is working and it turns on without problems I think shut off valve shouldn't be a problem, right?