Topic: Clear tube level, instant or takes time

[Ace Blackwell]

I have a 77 CB550F.  I checked my plugs a few days ago and they are black and sooty.  #3 was a little damp.  So tonight I did the clear tube test.   I used the outside meeting line of the body and bowl as 0. 

1 =  4.7mm below line
2 =  4.0mm above the line
3 =  8.7mm below line
4 =  2.25mm above the line

There are some adjustments to be made but had a couple questions

1) When performing the test, is the gas line supposed to be instant like a quick second or two.  Or in my case the tube filled half way in a snap, but the level kept rising.  It took about 15-20 seconds to reach a level and stop.  Is that normal
2) If I have two levels over the line, and two below, why are all four plug sooty?  From what I could read its a rich gas/air mixture.  Does that mean my air screw is set wrong and allowing too much air into the mix?

Thanks

[ckahleer]

If your starting point was with empty carb bowls, 15 -20 seconds is about right for the bowls to fill.
Are the readings you posted repeatable?
I suggest doing the clear tube test with the engine running. Revving it now and then. This will allow burn off of any carb over fill and determine where the float valves are actually regulating fuel height.

[flatlander]

to start with, set the level to the correct height (2-3mm  below gasket surface).
only after that, address your a/f mixture. assuming a stock setup that hasn't been tinkered with, put the air screw to its stock setting and then check again.

[Ace Blackwell]

Thanks all,

Yes the bowls were empty.  I would shut the gas off, pull the plug, (bowl would empty) put in the tube and turn gas back on.   So that's one piece of good news.  The test isn't way off.

I haven't adjusted the air screws but they aren't stock.  I rebuilt carbs end of last year.  I put screws at 1.5 turns from bottom.   

The test was repeatable but would like to try again just to be sure. 

Look like I chose the wrong marker.  When you say gasket surface, I assume you mean the gasket surface of the bowl before the gasket is installed?   

[robvangulik]

You wrote about 4.7, 8.7 etc. but half a mm. doesn't really matter. If you were able to look in the float bowl with the bike running (and especially fast over uneven ground), the fuel surface is comparable to a sea in a heavy storm, and still the bike will run okay!

[flatlander]

Look like I chose the wrong marker.  When you say gasket surface, I assume you mean the gasket surface of the bowl before the gasket is installed?
[/quote]

yes the top edge of the float bowl. as rob says, fractions of a mm don't matter. but the levels should all be +/- 3mm below that edge.

when you rebuilt the carbs, i hope you cleaned and re-used the original brass parts, instead of replacing them with some aftermarket stuff?

[ckahleer]

I have always felt float height is a bit overrated. If your within a few mm of recommended, good enough. Things like jetting, pilot screw adjustment, and needle height have much more effect on lean/rich. Even with the large differences in fuel heights you listed, all plugs indicated all cylinders are rich.

[Deltarider]

I have always felt float height is a bit overrated.

Man, back in time we never worried about float heights. Whereas in this forum... it is an example of mass hysteria. It comes and goes in waves.

[seanbarney41]

float level is one of those things...if your float level is wrong and so is something else, you may never be able to get it right.  If your float level is wrong and everything else is right, it really doesnt make a ton of difference.

[Ace Blackwell]

Thx all. It’s good to hear the float levels are a little more forgiving than I first thought.  Think I’ll mess around with them to get them at or below the gasket surface so I don’t have gas running from overflow. Then I’ll move on.  Even if they aren’t perfect.

[flatlander]

Man, back in time we never worried about float heights. Whereas in this forum... it is an example of mass hysteria. It comes and goes in waves.

back in the day you had the original parts in the carbs and didn't touch them because they just worked. now people replace stuff with aftermarket crap or pull things apart and put them together differently... and then the troubles start 

[PeWe]

I had float issues with my smoothbores. 1mm over making idle to a stinking smoking inferno. Plugs sooted pitch black in a minute.
So fuel level not overflowing is the 1st step.

Too high levels can hide a too lean setting at higher throttle lifts causing expensive issues.

Clear tube the only way to know its right.
Measure floats and bend them according to a specific height is how to do. Clear tube will show how it works. Are floats not moving freely or float valves leaking....

My CB750 K2 has my old K6 carbs with all jets original, except for main jets.
100.000km no reason for replacing any of them, float valves included.