Carb: Float Height Theory Question.

[deadbanana0717]

Hey guys...


I'm just about to install a set of Factory Pro Needles/Jets & Velocity Stacks... I'm reading through the instructions e.t.c.


Their recommended Float Height is 9.5mm.


I went through a few articles to get a better understanding of the theory, as another gentleman had mentioned his floats were set at 7.0mm. I was just wondering if there were any advantages to wards a higher or lower float height.


http://www.r1-forum.com/forums/showthread.php?p=5182637&highlight=float+height#post5182637


" The height is in mm. Flip your carb bank upside down and measure the height of each float from the gasket base. They should all be the same. Higher = leaner and lower = richer. "


Q: Is Higher = Leaner = Better Atomization? Lower = Richer = Poor Atomization
- like sucking out of a straw?


http://www.allthingsmoto.com/forums/f-15/how-set-your-motorcycle-carburetor-float-level-13609/


Explains Floats, but does not get into the theory of high vs. low.


Thanks!


Cheers!

 

[Brian P]

Too-high float level will raise the pressure across the metering jet relative to intake vacuum, causing more fuel flow (i.e. too rich). Too-low will do the opposite. At high engine load, the intake vacuum is the predominant source of pressure across the metering jet and the effect of gravity is not so significant, but at light engine load, there is very low vacuum and on top of that, the engine is not drawing as much air, so the float level has a very strong effect.

If you have a situation where the engine is too rich down low and too lean up top, or vice versa, you can use non-standard float level to influence this a little bit, but the problem is that the effect above separately affects the slow and main jets (and you can't have different float levels for each, because they're all pulling from the same bowl). Don't go too far from stock specs, because eventually you would get to a situation where it won't flow enough fuel to let the engine start (for low float level) or won't shut down the fuel flow far enough to let the engine idle without being too rich (for high float level).