Le Mans IV 1985 left carb leaking. What to look for first?

[thierry roullier]

Symptom: when one of the petcocks of my bike is open and the engine is not running, gas starts to leak from the left carb via the air filer. When running no issue.

My knowledge of carbs is limited to Bing carbs and I have yet to grasp the concept of a "pumper carb".

As a first assumption, I am thinking that the floater may not functioning properly as a first try. No matter what I will be replacing all the fuel lines.

Before I remove this carb and start inspecting, and while it is still on the bike, is there something I should be looking for?

 

[tatooman56]

Float sticking

 

[V700Steve]

If it is not sagging or hanging down in back, most likely float adjustment needed.. Could need new float needles, they have a very thin little spring inside them and a pin sticks up. The pin can wear from use. They could be all gooed up also.
Float Hieght for PHM's 17.5-18.5mm

 

[john zibell]

Also check that the float on that side is not heavy, or has had fuel leak in. Considering the age of the bike they may need replacement.

 

[SimonD]

And when you find the cause, replace the bits on both sides…

about two years back, I completely stripped and rebuilt my carbs (second series LM of 1977 vintage). I have an ultrasonic bath so they were washed in that, and I replaced all the o-rings, needles, jets and float valves, pump diaphragms, choke plungers & gaskets.

it was a satisfying & enjoyable exercise, but I’m not sure it changed very much! Perhaps it put off the day when something would have gone wrong.

 

[thierry roullier]

Thank you all. Very much appreciated. I will probably adjust and change the floats plus float needles. They do get heavier with age. As I may sell this bike I would not want to pass the issue to the future owner.

 

[scottmastrocinque]

Point to ponder…

I rebuild literally a hundred carburetors at least per year.

The most important thing you can do to prevent what you are experiencing, is the remove the carburetors, and polish the fuel stop barrel to a mirror polish inside.

I accomplish this by putting a cotton swab, like the kind you use to clean your ears, into my cordless drill, I use some high quality metal polish, and go to it polishing the inside of the barrel.

I then hand polish the fuel stop pin with some metal polish paste and a towel. I make sure that both parts are impeccably clean and shiny. The stop pin never sticks in the barrel if you have this type of polish on their surfaces.

Maybe these might help too…especially videos 6 & 7.

V50 mk2 Running on 1 cylinder Please help please

What does concern me is your fuel stop needle. That thing is absolutely filthy. You need to meticulously clean that puppy with the vinegar and a little metal polish on a cotton swab or soft towel. Then, you need to put some metal polish on a cotton swab and polish the inside of the carburetor...

www.guzzitech.com

 

[Amboman]

Thank you all. Very much appreciated. I will probably adjust and change the floats plus float needles. They do get heavier with age. As I may sell this bike I would not want to pass the issue to the future owner.

Unless the original floats are leaking (unlikely since Dellortos of that period used a solid, black float), I would not recommend replacing them. The current offering of Dellorto floats are white plastic and hollow. They are prone to filling with gas and causing running issues.

Another thing to check for interference between the float and the carb body at the pivot pin. I've seen floats drag on the carb body enough to stick. A little work with a jewelers file to remove some material from the float and all was well again.

 

[thierry roullier]

OK now I understand what is meant by floats "leaking" coming from Bing where the floats are some kind of aggregated cork that are not hollow.. I will consume all the material before touching this great bike! Very grateful to all who took the time to respond.

 

[john zibell]

OK now I understand what is meant by floats "leaking" coming from Bing where the floats are some kind of aggregated cork that are not hollow.. I will consume all the material before touching this great bike! Very grateful to all who took the time to respond.

The main problem with the Bing floats is that over time they absorb fuel. They are really bad in countries that have ethanol blended in their fuel. To this day Bing does not produce ethanol resistant floats.

 

[thierry roullier]

Point to ponder…

I rebuild literally a hundred carburetors at least per year.

The most important thing you can do to prevent what you are experiencing, is the remove the carburetors, and polish the fuel stop barrel to a mirror polish inside.

I accomplish this by putting a cotton swab, like the kind you use to clean your ears, into my cordless drill, I use some high quality metal polish, and go to it polishing the inside of the barrel.

I then hand polish the fuel stop pin with some metal polish paste and a towel. I make sure that both parts are impeccably clean and shiny. The stop pin never sticks in the barrel if you have this type of polish on their surfaces.

Maybe these might help too…especially videos 6 & 7.

V50 mk2 Running on 1 cylinder Please help please

What does concern me is your fuel stop needle. That thing is absolutely filthy. You need to meticulously clean that puppy with the vinegar and a little metal polish on a cotton swab or soft towel. Then, you need to put some metal polish on a cotton swab and polish the inside of the carburetor...

www.guzzitech.com

THank you these videos are really good. I will ensure that the fuel stop can fall off the barrel easily. Love Ohio!

 

[scottmastrocinque]

You are very welcome. I’m pleased they helped you.