Topic: 78 550K leaking fuel after carb service

[DaveBarbier]

Someone mentioned the floats are “solid” yet to float they must trap air in the solid material to float.

To float, an object only needs to weight less than the amount of fluid it displaces. Doesn’t have to contain air at all. Even an anvil will float on a sufficiently dense liquid like mercury.

[BRG-BIRD]

Gasoline is not very dense at all.

[flybox1]

I would move your floats to different carbs to see if the problem follows the floats. Someone mentioned the floats are “solid” yet to float they must trap air in the solid material to float, they can absorb ethanol and become too heavy.

Buoyancy...and yes, solids can float.

The black floats are solid.  Let me find my broken one.....

[DaveBarbier]

Gasoline is not very dense at all.

Yet it doesn’t require air to be inside something for it to be able to float. That’s all I’m saying. I don’t think these black floats can get fuel inside them. I think they’ll always float.

[BRG-BIRD]

Well just trying to help based on real experience. You should though ask yourself why does one type of solid wood weight more than another? Why does it not always float after being in water for an extended period of time? Is metal solid? Could it be porous?

Anyway hopefully the OP will get his bike up and running properly soon.

[TwoTired]

Material science has recognized that a given material can be more or less dense WITHOUT having air incorporated.
Yes, some materials can have air in them.
Many floats in carbs are made of a man made material, and it is not organic.  I've never seen a plastic float in an SOHC4 sink because it soaked in fuel to change it's boyancy.

Gasoline is lighter than water and floats upon it.  This is because it's molecular structure, makes the substance lighter than more densely compact water molecules.  Interestingly, water can hold air in suspension.   Gasoline still floats upon it.

Cheers,

[DaveBarbier]

Well just trying to help based on real experience. You should though ask yourself why does one type of solid wood weight more than another? Why does it not always float after being in water for an extended period of time? Is metal solid? Could it be porous?

Respectfully, for a better understanding of buoyancy I suggest auditing an 8th grade science class.

[brewsky]

  Even an anvil will float on a sufficiently dense liquid like mercury.

That analogy will be hard to forget!

[DaveBarbier]

  Even an anvil will float on a sufficiently dense liquid like mercury.

That analogy will be hard to forget!

Cody’s lab makes great videos!

[flybox1]

These last few posts were a good chuckle...

I always remember the photo from grade school of a British pound coin floating on top of Mercury.

[brewsky]

Here is what the float looks like immersed in gas and how the fuel level translates to the outside of the bowl.

This is with the float set at 14.5mm per '78 spec. for 750K

The level may be a millimeter or 2 off due to measurement error

Note these are from a 750, but the 550 carbs are similar

[BRG-BIRD]

Let's see what the OP comes up with. I have no problem being an outlier which can flip some out, a little out of the box thinking doesn't hurt.

[calj737]

stick your thumb on the overflow hose,if the seats are leaking the carbs will fill up and leak elsewhere,if it stops you have very fine cracks in those brass overflow tubes.

Also referred to as the "Little Dutch Boy" test 

[dave500]

why didn't strynboen or deltarider mention it then?

[spanners]

Because sticking your fingers in Dykes, no matter what the emergency is probably banned by H&S regs these days in Holland