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Float level question.

ntklr650

Matt6:34
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Michael
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How does the float level effect how rich or lean the bike runs. Ultimately it effects it at the extremes but is your adjustment actually setting your richness?
I'm just confused and could use some clarification.
Thanks

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Float height generally does not effect richness or leanness as drastically as the other components in a carb do. That is more determined by the jets, needles, and air metering screws. Float height controls the level at which fuel flow into the bowl is activated and deactivated. Set it too low and you can starve the bike for fuel, set it too high and you can have a problem at the needle valves.
 
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Float height generally does not effect richness or leanness as drastically as the other components in a carb do. That is mainly determined by the jets, needles, and air metering screws. Float height controls the level at which fuel flow into the bowl is activated and deactivated. Set it too low and you can starve the bike for fuel, set it too high and you can have an overflow problem.

I agree mostly. but float height does factor into carb jetting. The popular Factory Pro needles that were made for carb'd 950 KTM Adventures back in the day had detailed instructions on fine tuning jetting using float height. That company really thought float level was an important component.

The general rule is that higher fuel levels in the float bowl (Which physically is a lower number float setting) can give you richer overall settings, and lower fuel levels leaner. You can really feel this on a two stroke dirt bike when the gas level gets low, then lower, etc. the bike leans out for the minute before it runs out. That is an extreme example but the engine does run progressively leaner as the fuel level drops.

At the end of the day, set your float level within the parameters as Tim suggests, and jet from there. That will get 99% of all of us where we need to be.

My 950 Adventure does tend to splash fuel out of the overflow even at factory settings, so the conventional wisdom for that bike is to use a lean float level and then go richer on the mains a step or two, and maybe lower (rich) the needle clip one step too.
 
Thanks for the advice. I had a guy at work telling me that you set your richness with your float. I tried to tell him it is your needle and other things but he insisted I was crazy. I guess the real telling sign is that my bike runs and his does not.

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I guess, in a sense, float level can affect richness and leanness. If the level is too high, it'll flood the engine with raw fuel. Too low, it'll starve the motor for fuel.
 
Factory Pro said:
...
CV Carbs: Too RICH at full throttle / low rpm (that's the most common in CV carbs)
Slide carbs (FCR's) - Float height controls 25% throttle at ALL rpms.

If the float height is too low (small float height measurement), bend the tab slightly to increase the height measurement. It's a 5:1 movement ratio.

CV: If the float sticks out further, down, into the float bowl, the carb will deliver less fuel (leaner), especially at low rpms and at cruise.
Slide carbs: Float height controls 25% throttle at all rpm's, even at redline.

You'd generally change the float height in 1mm increments when tuning. It will affect the topend slightly. Maybe 1.5mm leaner float height would require 1 size larger main jet to keep equal main jet fuel delivery.


CV Carbs: Too LEAN at full throttle / low rpm (not too common in CV carbs)
Slide carbs (FCR's) - Float height controls 25% throttle at ALL rpms.

If the float height is too LARGE, bend the tab slightly OUT to decrease the height measurement.

If the float sticks out further, UP, into the carb body, the carb will deliver MORE fuel (richer), especially at CV low rpms and at cruise.

It will affect the topend slightly. Maybe 1.5mm richer float height would require 1 size smaller main jet to keep equal main jet fuel delivery.

You'd generally change the float height in 1mm increments when tuning.

When you are done, a multi-cylinder must be all within .5mm (1/2mm) or .020" range of each other.


The level in the float
chamber is therefore a calibration
element of the carburetor, since the
metered fuel delivery changes with
float level, and therefore affects the
mixture ratio. By having a high
float level, a greater fuel quantity is
delivered compared to the case with
a low float level, under all operating
conditions and for all of the carburetor's
circuits.
...
 
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I have been measuring the float location when I rotate the carb till the needle just seats. I believe it's about 0.60 from the flange to the bottom of the float on the KLR.

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How are you measuring the "fuel" level? It should be done dynamically using a clear tube connected to the drain on the bowl, held up to the side of the carb and visually inspected to the manufactures spec.

https://www.justanswer.com/motorcyc...m-2002-yamaha-raptor-80-mikuni-carb-fuel.html

I would counter with--It should be checked the way the manufacturer specifies. For example, for the KTM 950 Adventure, there is a factory tool (a template) that measures float height exactly. I have templates in three different heights to easily measure different float heights.

I have never seen (I certainly could be wrong) an OEM recommend whatever it is you are linking to, although maybe it works great for a Raptor 80 mikuni carb.
 
I have been measuring the float location when I rotate the carb till the needle just seats. I believe it's about 0.60 from the flange to the bottom of the float on the KLR.

Sent from my Moto G (4) using Tapatalk

17.5 mm is the factory height you are probably already aware of, so you are pretty close. I'd use MM as my measurement instead of inches. 17.5mm is right at .69 inches.
 
17.5 mm is the factory height you are probably already aware of, so you are pretty close. I'd use MM as my measurement instead of inches. 17.5mm is right at .69 inches.
After I set it, should I fool with a clear tube connected to the bottom to adjust further. I have always set it on both of my KLR's and never had an issue.

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After I set it, should I fool with a clear tube connected to the bottom to adjust further. I have always set it on both of my KLR's and never had an issue.

Sent from my Moto G (4) using Tapatalk

I wouldn't, but that is just my opinion. I certainly am not the Wizard of Oz. The way you described measuring it is by the book, so if you are confident in your work fire it up and go ride.
 
John, that has been a common method for years with some street bike
guys as on an inline four using the slack tube method is easier than pulling
a rack of carbs and airbox off a bike

Is it perfect? probably not, will it be close enough? It should get you fairly close
 
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