k75RT, Massive fuel leak at idle, not off

[atarifan2600]

I've been off the brick for a year or two because it's been a disheartening repair experience.
Some of this is going to be faulty or incomplete due to my memory, but:

I had relatively recently replaced the fuel sender unit and o rin gasket and such in the tank.

When the bike is not running, with a full tank of gas-  it will not leak a drop.

It fires up and idles beautifully.  I think I gave it a few revs and it respondes as expected.

But after about 10-30 seconds, suddenly there is a GUSHING amount of gas pouring out of the engine, and I haven't been able to determine where.
It's not pouring from the from the front of the tank to the front of the fuel rail. It's not coming from the back of the rail.
but when it's pouring, all I can tell is that fuel is pouring out over the engine, and I can't pin down the source. 
From the bottom of a pressurized tank?
From the regulator?
Something in the throttle bodies?


I've finally just taken the  fairing apart, and the regulator out. 
THere's plenty of indications that there's a leak somewhere on the back of the plenum, but I'm not sure from where.
The fuel lines in and out of the regulator seem solid.
The vacuum line holds vacuum, but I am not sure how to test the regulator itself.
The little S-shaped return hose, but that seems to hold pressure and not have any noticeable cracks.
other than that, I don't know where I'd look a tthis when it's running and fully assembled, as the bike seems to be built fully around whatever is leaking.


any suggestions on what to look at?

[Laitch]

If fuel is gushing out, that indicates fuel under pressure. Cracks in the floor or right rear port mounts beneath the tank could be the culprits. If fuel is pouring out, the fuel return line attached from the fuel pressure regulator to one of the ports on the left front of the tank could have cracked open somewhere along its length. I believe the return line is more likely the source.

[atarifan2600]

Thanks- as long as I was firing the parts cannon at this, I picked up more parts than I needed.
regulator
fuel line
vacuum line
breather hose
Regulator


Getting the airbag off is a pain in the ass, getting all the farings off is a pain in the ass, but doing them both at the same time really makes it a bummer.
So I'd rather not touch it more than I need to.
Once parts get here, we'll see what happens.  I should probably pressurize the tank and see if it's showing a leak- but I don't think it is.

[Laitch]

Did you remove the hose connected to the tank and the fuel pressure regulator (the fuel return line) and inspect it for cracks, leaks or obstructions before you fired the cannon?

[atarifan2600]

Return line -front port on the front of the tank- to the top of the regulator looked good.
Regulator to the back of the fuel rail- clamped and looked good.
Supply line from front of the rail to the rear port of the tank- looks good.
S-shaped Breather line - supple, holds pressure, no cracks


So those are the main components I'd checked and re-checked, and am at a loss about.

O Ring on the bottom of the tank is one obvious next step.


What about the two relief  valves?
One's for rain on the outside of the tank.
One is venting pressurized air from inside the tank.
Both point downwards into the collector cup.

Is it possible my tank is pressurizing and pushing gas out of the line connected to the tank somehow?

It feels like extra air should just escape out of the bottom of the tank and down the 'collector cup', and I should never be in a position to pressurize the tank and push gas up and out of it.  We'll see what happens when I re-assemble it all. It'll be easier to see now that it's approaching naked bike status.


http://www.motobrick.com/index.php?topic=6495.0

[daveson]

The supply line should go to the front of the fuel rail, not to the regulator.

[atarifan2600]

Thanks- corrected my descriptions.

Return though the regulator, supply from the rear barb to the front fuel rail.

Got it!

[Laitch]

The two outlets into the cup shouldn't have relief valves. Water comes from one and vapor comes from the other. The tank vapor relief port was formerly connect to a hose that had a valve when the hose was coupled to an intake port on the crankcase. The valve should be long gone by this time.
You referred us by link to a comprehensive discussion on the siphon effect. Does your Brick's tank have the oblong vapor chamber mounted on the roof of the tank near the tank's opening?

[atarifan2600]

Yes, it’s got that oblong chamber with a barb; nothing connected to it.

I’ll have to see what happens when it’s running again, but all of the rubber hoses seemed both clamped and not-cracked (as in actually holding pressure), so I’m not sure where the gas would be coming from.

Tank doesn’t show any evidence of paint damage or pinholes in any of the corners that would make me suspect a leak directly from the tank.

[Laitch]

I’ll have to see what happens when it’s running again,. . .

That's a plan. When it starts leaking, open the cap and see what happens. Eye protection and fire equipment recommended.    The hose connected from the chamber stub pipe to the pump filter basket—if the pump doesn't have a filter sock—seems only to be necessary if the tank is run so low on fuel that air bubbles from fuel agitation can enter the pump to damage it. The pipe presumably evacuates that air from the filter through the hose to the chamber and out into the atmosphere through the metal pipe attached to the chamber that exits through the floor of the tank.

[nadrol]

I redid all of the fuel line on my newly acquired k1100 in June, but apparently the hoses softened over time and I found fuel all over my left foot suddenly shortly after startup one day recently. The band clamps under the tank were not tight and fuel was spraying out between the nipple and hose. I'm glad I used ear clamps on the regulator so I wasn't concerned about those.

Not sure this is applicable here, but it's worth looking out for.