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To adjust float
height: Sooo....
You read the
carb kit instructions and they specify a 15mm float height.
Float height? What's a float height? 15mm? How much is
that in inches? (it's .590")
Does that mean
I must do it???
YES!
Gee whiz!
What do I measure with??
You can use a
set of vernier calipers, if you have them - they are great
for measuring all sorts of things, but you can make it even
easier with our...
Float Level
Setting Gauge
Measures from
0mm to more than you will ever need!
Easier to use than vernier calipers on carbs. The vertical
legs adjust in width and the thin post slides up and down so
you can slide the post to the required clearly marked float
height measurement.
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Remove float bowl screws.
Factory Pro gives you replacement allen screws in most carb
kits to replace usual phillips screws. |
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Slide the lower movable leg
so that both legs will rest on what would be called the
gasket surface of the carb body (if there was a gasket,
anyway)
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Tilt the carbs
so that the floats just flop over towards and into the carb
body.
Tilt just
enough to touch and close the float the float valve, but...
Do NOT
compress the float valve spring when measuring (only
exception is 95-97 zx6r)
Test adjust the "L"
horizontal arm in the usual 1mm increments and test fit the
gauge to see what the float is set at now. (or not).
(If we say 15mm and you
measure 4mm less than that - you might be compressing the
little float valve spring.)
At this time, you can set the
Float Height Gauge to what you want to reset the floats to.
If you are tuning, you'd usually use 1mm increments |
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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. |
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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.
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Nifty baffle plates in the 05
KLX300! |
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This carb type has been
around since the early 80's! It's had some updates over the
years. It's similar to the Ninja 900'a and ex250 styles. |
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A view from the engine side,
butterfly open. |
Why adjust the float
height?
Changing the float height
changes the level of the fuel in the float bowl. The fuel height adjusts
the full throttle, 2k-3k rpm and part throttle cruise, as in cruising
around town, trying to be quiet... To give a scale of change, if the
bike runs well when cold, but gets a bit sloppy when fully warmed up,
lower the fuel level 1mm (i.e. go from 15mm to 16mm float height -
remember the float measurement is "backwards").
When do I adjust the float
height?
When installing a
Carb Recalibration Kit tm.
When rebuilding carbs.
To adjust low rpm / part throttle operation that isn't pilot jet, fuel
screw or needle height related.
When a bike starts running rich at low rpm after a mishap or
After an overwhelming gravity equalization process occurs.
How much is the nifty Float Valve Measuring Tool?
How much is that nifty Float Valve Measuring Tool?
About $49.95, direct from Factory Pro
415 883-5620
voice
415 492-8803 fax
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(for larger view, use your browser "view image".
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This is a picture of a set of
38mm Mikuni CV carbs as supplied on the:
Ducati 600/750/900
Yamaha YZF750, fzr1000
Yamaha TDM/TRX 850
showing the Float Height Tool in use.
Note: Doing 38mm Mikuni downdrafts?
Get the nifty float cage holder to make your life easy!
Click here
Note:
Measure the "rectangular", taller float (not the lower, "diamond /
parallelogram" shaped one) There is ~3mm difference between the 2
different floats!
Remember to measure the float height - tilt the carbs till the floats
just barely flop over and close the float valve, but don't compress
the float valve spring! |
