precision float level adjustment.

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jseng1

jseng1

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We've all adjusted float height by linear measurement. I did that with my carbs but I noticed that when I shut off the fuel - one side died about 20 - 30 seconds before the other.

So now I adjust the float level so they both run out of fuel at the same time (starting with same amount in fuel lines when shutting taps).
 
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Triton Thrasher said:
Height of the fuel is a linear measurement, not a period of time.
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Of course but when you make the best measurement you can and adjust each float height as close as possible and then find out that one carb still carries a bit more fuel - what do you do? You adjust again because what you want is the same amount of fuel in each bowl. Measuring the float position doesn't guarantee a specific amount of fuel - I used to think it did but maybe the float measurement isn't accurate enough.

This is especially a problem with carbs that have spring loaded needles.

What ever it takes to get balanced idling carbs.
 
I’ve heard of rigging visible fuel height indicators out of clear tubing, so you can see the height in a dynamic, functioning, mode.

Also the procedure, before bending/setting, of placing the carb body at the just so angle such that the float lever touches the needle is imprecise, mainly because it’s so hard to see but also because the spring inside the needle introduces another factor.

It seems like each carb has a range of heights that work well enough
 
jseng1 said:
Of course but when you make the best measurement you can and adjust each float height as close as possible and then find out that one carb still carries a bit more fuel - what do you do? You adjust again because what you want is the same amount of fuel in each bowl. Measuring the float position doesn't guarantee a specific amount of fuel - I used to think it did but maybe the float measurement isn't accurate enough.

This is especially a problem with carbs that have spring loaded needles.

What ever it takes to get balanced idling carbs.
Click to expand...

Surely The amount of fuel is irrelevant, it's the height of that fuel in respect to the bottom of the ifle jet (or port opening in the carb) that dictates the static pressure and the subsequent pressure differential required to draw the fuel into the intake.

For all intensive purposes you could have a swimming pool for a float chamber, as long as the depth of the fuel was the same across the carbs.
 
I am not a carb expert but have fettled many over the years, and I statically set my float levels. I agree that float level being relative to the jets makes sense.

There are discussions within these forums about similar floats having different buoyancy characteristics relative to fuel level--this could make nonsense out of statically measuring/setting float levels. It seems if the two floats react differently to the same amount of fuel in the bowl, the higher density float would require a greater amount of fuel in its bowl to close the float valve than would the lower density float. This would be one explanation why one cylinder continues running after the other carb runs dry.

~998cc
 
Someone should engineer a float pivot shaft with an eccentric that could be adjusted externally while the engine's running for dynamic testing.
 
In the case of Amal Concentrics, I favor fuel height over and above float height or float level.

Using a U-tube from the float bowl drain plug allows you to see exactly what is going on inside the carb with fuel and at the right angle.

It's quick, easy and accurate.

Plus Andover are now doing a little kit that makes it a no-brainer!

precision float level adjustment.

https://andover-norton.co.uk/en/shop-details/20569

Particularly with the new stay-up floats - I think the height measurements in the book are no longer valid.
The floats seem to sit higher on the fuel, plus they are adjustable by tweaking the metal tang.
 
gtiller said:
In the case of Amal Concentrics, I favor fuel height over and above float height or float level.

Using a U-tube from the float bowl drain plug allows you to see exactly what is going on inside the carb with fuel and at the right angle.

It's quick, easy and accurate.

Plus Andover are now doing a little kit that makes it a no-brainer!

View attachment 13951

https://andover-norton.co.uk/en/shop-details/20569

Particularly with the new stay-up floats - I think the height measurements in the book are no longer valid.
The floats seem to sit higher on the fuel, plus they are adjustable by tweaking the metal tang.
Click to expand...


I’ve just made one of these this very afternoon, took about 30 minutes on the lathe :)

Dave
 
The clear plastic tubes temporarily installed to compare fuel level in the bowl looks like the best option. If the levels are not the same then the carbs can run different mixtures even though they have the same jets. If you don't have a precision built carb like a Mikuni or Keihin then your levels are probably not the same.

This is what was happening with my carbs and I just figured out the problem - measuring the floats wasn't accurate enough.

Shutting off the taps with equal length fuel lines told the story.
 
Or stick it on a dyno and see what is happening on each side in turn. Fit some fuel level tubes as well and watch what happens.

Shutting the tap and then seeing what happens proves what happens when the tap is shut. It's what's going when the tap is open is what matters.

Krypton tuning a tractor comes to mind.
 
If you apply a U tube shunt between the carbs, as gtiller shows in Reply #10, the fuel level in both carbs will come to the exact same level, regardless if one float is slightly higher/lower to the other.

Slick
 
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Dellis said:
I’ve just made one of these this very afternoon, took about 30 minutes on the lathe :)

Dave
Click to expand...
I made a couple a few years ago when E5 started to appear and left them fitted to allow me to quickly drain the float bowls. They are held up by Mk2 Amal air vent tube clips.
So far so good.
Dave
 
texasSlick said:
If you apply a U tube shunt between the carbs, as gtiller shows in Reply #10, the fuel level in both carbs will come to the exact same level, regardless if one float is slightly higher/lower to the other.

Slick
Click to expand...

Until you lean it onto the side stand.
 
MexicoMike said:
Too much angst! These aren't Formula 1 motors. Set the float level slightly below the lip of the bowl and forget about it. ;)
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Exactly! That's how I set up the Premiers last year.

Interesting note: A new (non-balanced) exhaust was installed about the same time as the Premiers, and while the pipes are showing straw/yellow temper color near the head, the right side pipe is noticeably darker. Could this indicate a leaner mixture due to a slightly low float level on the right side? Perhaps I'm over thinking this... :confused:

~998cc
 
Triton Thrasher said:
Until you lean it onto the side stand.
Click to expand...

Do you ride it on the side stand?

When you lean it at speed, the fuel level remains exactly in the same geometry inside the float bowl, as it is when level.

This issue keeps coming up .... I will have to write up an explanation when I have more time.

Slick
 
texasSlick said:
Do you ride it on the side stand?

When you lean it at speed, the fuel level remains exactly in the same geometry inside the float bowl, as it is when level.

This issue keeps coming up .... I will have to write up an explanation when I have more time.

Slick
Click to expand...

I certainly have ridden off with the stand down, but that’s different!

I do park the bike on the side stand with the engine running, to adjust the idle and all that.

Even with the engine stopped, it would be unwise to forget to shut off the fuel, if the bike was leaning with one carb high enough to make fuel dribble out of the other carb.
 
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