Yamaha XVS1100 V-Star
6 only

True Rear Wheel HP

Carburetor Tuning Kits

FBK kit includes 2 larger filters as compared to the stock photo, here

CRB-Y41-3.0-FBK "FatBack"
inc. special BMC filters

28% larger than K&N!

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Well, well, well, then -
They took our "Big Air" name and used it......
So - We will do them 1 or 2 or 3 True HP better!

All Factory Pro Intake Systems are developed on real research level EC997 Low Inertia dyne systems using 4 gas EGA and 30 plus years of product development.
You'll NEVER see "tuned to an Air Fuel Ratio" product here.


The even bigger Big Air Kit!

Factory Pro has developed a kit that uses our own in-house designed, exclusive BMC Tapered Cone filter - Larger in area than the filters that other's use, they fit under the tank AND flow more - for best possible power - at minimum - more than the other current kits -
Use this kit if you want the most possible power - while still retaining excellent lowend and midrange, if properly tuned.
Use with aftermarket exhaust.
Retains best possible mileage AND best possible performance (when properly tuned!)

The carb has 2 "main jet" sort of items in the float bowl. One is in the area of 105ish and one is probably a #42.5. The #42.5 is the jet that controls the choke circuit and  normally, you don't change that one.



Carb kits

CRB-Y41-3.0    $109.95

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Config 30 -  Jet kit for REMOVED airbox  or "like" a Hypercharger.

Boosts power at midrange and full throttle more than when using the stock airbox, improves throttle response - excellent for improving throttle response and decreasing backfiring under decel. conditions.

Generally - improves power 5% to 10% over using the stock airbox.


CRB-Y41-1.0        $109.95

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Config 10 - STD drop-in carb recal kit

Boosts power a bit at full throttle, improves throttle response - especially at low rpm and part throttle, smoothing power delivery. Engine runs a bit cooler and usually smoother.
Excellent for improving throttle response and decreasing backfiring under decel. conditions.
Comparison to other kits: Improved driveability when properly tuned.

Repair / Tuning Parts



main jets
pilot jets
carb kit

While we try to include enough jets in our carb recalibration kits to tune stock engined bikes, sometimes you riders and tuners just can't resist tinkering for a bit more power - and that usually means that you need different pilot and or main jets.
We have them in stock and ship daily!

main jets

Pilot jets

Main jet  #221 small, round slotted
Main jet #604 large round slotted
Main jet other types available  .
Pilot jet 30/96 emulsion type
Pilot jet  151/067 non emulsion type


TL-float height

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The only way to accurately measure float heights. Works on nearly every carburetor.
More information on how to set floats, resultant fuel level, it's effect on low rpm fuel delivery, pictures.....
Float Height Page

This Carb Recal Kit developed on the same EC997a Eddy Current dyno that developed the K59-1.7-RK ZX6r RaceKit (Muzzy and Kinko's choice), the Y73-1.7-RK YZF750 (Vance and Hines choice), S37-1.7-RK GSXR750 x, Suzuki of France and most of America's privateer racers choice)...

Tech Tidbits

Float Height Measuring
Needle Jet wear
(sometimes called "worn emulsion tubes)
Inspect your brass needle jets for wear when you take out the needles. If the needle jets have oval wear pattern, they will allow excess fuel to pass by the needle causing excess low speed richness.
The fuel will also consist of large drops, rather than small drops. Large drops of fuel tend to drop out of the airflow and not burn.
Check out Tech Section for "Needle Jets, Mikuni, worn"


Go to General Technical Support

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???

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.

Remove float bowl screws. Factory Pro gives you replacement allen screws in most carb kits to replace usual phillips screws.

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)

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 guage 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 Guage to what you want to reset the floats to.
If you are tuning, you'd usually use 1mm increments

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.

Nifty baffle plates in the 05 KLX300!
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.
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

415 491-5920 voice

415 492-8803 fax


carb,float adj,38Mik.jpg (197016 bytes)
(for larger view, use your browser "view image".

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

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!