Click image for larger version  Name:	NeedleValve.jpg Views:	1 Size:	8.6 KB ID:	5250NEEDLE VALVE SET REPLACEMENT

Reason for changing the STOCK needle float valve set

I own a 2000 Silverado, and love this bike. Shortly after I had the bike broken in, I decided to see what our rides could do flat out. Well at just under 100MPH, the bike stuttered a bit and began missing. I attributed that to the “REV LIMITER” kicking in. To make a long story short, this spring, still with the same bike, but now with Samson Shogun 2 ¼ inch full pipe system and Küryakyn twin velocity breather, perfectly jetted, I seemed to be hitting that so called REV LIMITER earlier. This caused me to investigate this problem further.

After sacrificing ride time and some cash, using my own ride as test vehicle … You can read the post to follow the history;

Here is the conclusion. Our Mikuni 40mm CV type carburetors have a 2.0 flow size needle valve set. This corresponds to 2.0 mm hole size, which also equals a 200 DynoJet size. Once you add up all the orifice sizes that fuel leaves the bowl from and compare it to the only entrance size of the needle set, you find that the MAX inlet capacity is just a bit under sized to the MAX consumption limit. Most will never run there ride in this situation, therefore will never “starve” the bowl. But, anybody who’s modified there bike requiring increasing the fuel capacity to the engine, i.e. larger jets, should strongly consider replacing the needle valve set of the carburetor bowl. We re-jet the carburetor to make sure our fuel mixture stays correct, in order to maximize the performance and to NOT lean out the engine and endanger it, but we forget another component in the fuel delivery system, maybe as important, if not more, the needle valve set!

Ah yes, as a BONUS, if you swap the needle valve set with this larger one, the fuel pump becomes unnecessary! That’s right, you don’t need it anymore.

I would like to also mention and give a special thanks to Joel (Odo) Parker for his help and assistance in double testing and confirming the test results. Parts required

#2.3 13370-07F00(Suzuki p/n) (old p/n 13370-19E00)
#2.5 13370-08F50(Suzuki p/n) (old p/n 13370-08F00) ← This one recommended.

Yes these are Suzuki part numbers, but or carbs are manufactured by Mikuni, who also also makes carbs for Suzuki and this needle valve will interchange with ours. The 2.5 is recommended for running with NO fuel pump.

UPDATE: (April 2015)

It is now recommended to use the 3.0 mm float valve, part # - 2C6-14190-30-00, that is used on the 2002-2008 660 Yamaha Grizzly instead of the Suzuki float valves Procedure

Note: Depending on your bike set up, carburetor bowl access may require you to remove your carburetor from the engine.

1. Shut off the tank fuel petcock and then drain the carburetor bowl. Remove your air filter, if required, to gain access to the bowl (float chamber) of the stock carb. You may need to loosen the carb heater (item 2) with a 10 mm deep socket, in order to swing the electrical ground tab (item 1) out to allow the cover to come off.

bottom view of carburetor
Bottom View of Carburetor

2. Remove the 4 holding screws.

Bottom View of Carburetor
Bottom View of Carburetor

3. Remove the float holding screw (arrow). Be careful not to drop the pivot shaft (item 2), it can slip out easy. Be very careful NOT to loose the needle that will come out with the float assembly tab. Carefully put the float away making sure NOT to damage, scratch or bend the TAB on the float assembly.


floats reference
Floats Reference, Bottom View

float picture

4. Remove the needle valve body by removing the retaining screw first. The brass valve body will not fall by itself, you will have to pull it out with needle nose.

Floats Reference 2Valve Body

5. Moistened the o-ring on the NEW needle valve body with a light oil or Vaseline. Carefully push it in the carburetor. Fasten in place with the retaining screw, DO NOT OVER TORQUE! Snug is good enough.

6. Reinsert the float assembly with the new needle. It should slide in easy, do not force or fight with it. DO NOT OVER TORQUE the holding screw for the float shaft.

7. Re-install the bowl cover making sure both o-rings (item 1) are in place and not damaged. Again, tighten the bowl cover holding screws snug; do not over torque as you may strip them. You may want to get 4 NEW M4-.7mmx10mm screws, depending on the shape of the ones you have. If you’ve already rejeted your carb, you probably have already changed out the stock Phillips head screws.

float bowl

8. I would recommend, especially if going pumpless is desired, to remove the plastic screen mesh in the gas inlet spout of the carburetor. Remove hose (item 1-PIC 1), screw in the spout (PIC 2) a small wood screw until snug, and then pull it out with pliers, with the plastic mesh. Reconnect the fuel line.

fuel line
Fuel Line Into Carb

Fuel Spout on Carburetor
Fuel Spout on Carburetor

9. THIS IS THE MOST IMPORTANT PART, make sure to set the bowl level correctly, as per Mr. Tidy’s procedure on the Road Star Clinic;

If you’ve removed your carburetor from the bike, it may be just as easy to set the float bowl right on a bench (or kitchen counter as I’ve heard some do, lol), with water. You want the fuel level distance to be anywhere within a 2 mm gap from the bowl seem down, on a level standing carburetor.

This is the recommended setting for 99-03 Road Stars ONLY. 04s and higher have their float level set higher than the mating surface. If you have an 04 or later model, check the service manual for correct float level settings.

“Float level can be too high or too low and that effects any, or all, jetting parameters. A high fuel level richens the mixture and a low level can lean it.” – Extracted from an article here on the Clinic by Ken "The Mucker" Sexton.

{hyperlink this] Principles of Modern Motorcycle Carburetor Function

10. Once done, don’t forget to tighten up the heater, BE VERY CAREFULL not to over tighten. The heater is hollow and made of brass, it can snap very easy! Snug is enough.

EDIT NOTE: If you are going pumpless, route the fuel line carefully away from the cylinders to avoid line melting. I used the spring wrap from the stock fuel line and wrapped it from the carb up to the petcock. The important thing here is to make sure the spring wrap covers the part of the fuel line that could potentially come in contact with the cylinders.

You are now done! Enjoy the ride and ride as hard as you want, you will no longer get stutters at WOT (wide open throttle) as the fuel can now enter the bowl at a MAX rate slightly higher than the MAX demand from it!