Fuel Leakage Problem

[Graeme]

I was caught out today riding by running out of fuel and found petrol pouring through LH carbie. Switched to reserve & stopped at a garage & removed the fuel bowl and lifted the float which stopped the flow so that function seems OK but on replacing the fuel bowl, the problem remained. Got home cursing every red light.

Could the floats have expanded over time perhaps contacting the side of the bowl preventing the float operation? I should check the RH side & check for any difference. I'll do that tomorrow; I've just been abused for coming in stinking of petrol. (They don't care, you know; they just don't care.   )  

[Barry]

I don't think the floats expand but some say they get heavier over time. Could be the float sticking or just be dirt in the valve seat. I would remove the float and valve for a general clean up. The conical rubber tip on the end of the valve needs to be in good condition and the seat clean. Take note of the tiny wire clip on the other end of the valve to make sure it goes back the right way.

[Yikes]

Graeme,
 
Your leak was most likely caused by some crud in the fuel making its way to the float valve causing it to stick.  If it happens again, check the bottom of the float bowl when you have it apart and see if there is anything in there.
When I first got my bike, I experienced the same thing and discovered my fuel line was deteriorating on the inside, sending little bits of black stuff into my carbs.  The fuel line looked perfectly fine on the outside, but you could see cracking on the inside.  Since then, I've followed Rob's advice and replaced my fuel line yearly.

John Mc

[Bob_Roller]

The OEM BMW foam floats have been known to absorb fuel over time and get heavier as has been mentioned already .

I had the hinge pin that the float pivots on back out and cause the float to hang up a bit .

I've also installed an inline fuel filter, as I was getting a fair amount of gritty sediment and water in the float bowls when they were removed for cleaning .

I've never had a problem with the fuel line causing problems, but several members here have reported fuel line deterioration causing float problems .

[montmil]

Even money it's a bit o' grit in the needle seat.

Examine the rubber tip on the float needle for clues; such as a rough spot or 'crater' from some griity thing.

Do you run a fuel filter?

Monte

[Graeme]

Yep, I've got a fuel filter. It works fine manually i.e. if I lift it with my finger, the fuel shuts off. I actually used the word "leakage." it actually just pours out of the carbie seemingly unhindered.

Thanks for the advisies, I'll try & get to it this morning.

[nhmaf]

Could be the floats are old and now "sinkers" instead of "floaters", or hang up with the pin/clip or problem with the needle tip or particle obstructing it.   You might try also examining the metal tabs to which the floats on the other carb attach and see if the flooding carb has the same 'bend' - if the floats are still at least somewhat floating, a light bend may help get the needle to close.   But, too much of a bend can mess with the fuel level in the bowl and cause high speed/open throttle starvation.

[Graeme]

Well, embarrisingly, today I replaced the needle. That's it. Just replaced the needle. Turned on the fuel tap & no leak. Kicked over first go.

It's embarrasing because it's taken so long. Work, just been travelling almost constantly.

Tomorrow, I go for a ride.

[Rob Valdez 79 R65]

The needles have rubber on the tips that gets hard over time.  They should be replaced periodically.  10 years or so?  Especially in extremely hot climates or countries that put their nation's fuel supply ahead of their food supply.  

[montmil]

Well, embarrisingly, today I replaced the needle. That's it. Just replaced the needle. Turned on the fuel tap & no leak. Kicked over first go.

Farm implements, they are. Gotta love 'em. [smiley=cowsleep.gif]

Monte

[Graeme]

Ah! (rude word). Took it out looking for a nice four hour run down the coast on the first fine day for a while, problem came back & just got home on one cylinder the last killometer.

Looks like a full reco of the carby...

EDIT: there's a "safety clip" on the old needle but none supplied with the new one. It loops over the lug on the float. Just wondering if that pin was dipensed with. It doesn't seem to serve any purpose & might be jamming.

[Barry]

there's a "safety clip" on the old needle but none supplied with the new one. It loops over the lug on the float. Just wondering if that pin was dipensed with. It doesn't seem to serve any purpose & might be jamming.  

The purpose of the clip is to pull the needle down in case it should stick on the seat. Clips of his type are not peculiar to Bing carbs.

I think some people do run without them.

We had a discussion on this previously http://www.bmwr65.org/cgi-bin/yabb2/YaBB.pl?num=1280925209/4#0

[tvrla]

Are you getting any particulates through from the tank? Doesn't take much.

I had a problem like yours once that took a while to discover. Turned out that the metal end of the needle that works against the float tang had rubbed a channel in it. It had gotten bad enough that the float then hung up and would jam the needle sideways, preventing it moving up and closing off the flow. Check the tang to see if something like that didn't happen.

I decided to prevent that happening again by chamfering the sharp edges on the float needle. I also smoothed out the gouge in the tang and all was good.

[Graeme]

I pressed the float up against the new needle with considerably more force that could be effected by floating but much less than could cause any damage & the flow stopped.

So, I guess it's the seat where the needle sits.

My manual (Haynes) isn't particularly clear on that area. (Maybe me)

[Barry]

So, I guess it's the seat where the needle sits. My manual (Haynes) isn't particularly clear on that area.

It wouldn't be. The valve seat is not commonly replaced nor is it an easy job being an interference fit in the carb body. If it doesn't seal easily with a new needle maybe there is some damage to the seat that can be polished out.

If you really have to replace the seat I think one method  of removal is to drill and tap the seat so you can construct a little slide hammer to extract it.