This article shows the cleaning and race preparation of a set of Yamaha R6 carburetors; however, this information may be useful for all makes of carburetors used in Micro Sprint car racing.

In my fifteen years of experience with Micro Sprint car racers, I have determined that one of the most overlooked maintenance items are the carburetors.  Time and time again I hear competitors complain about inconsistent engine performance.  The first question from my mouth is: “did you clean the carburetors?” and more often than not the answer is “no” or “not for a few weeks”. 

I believe that many racers are slightly intimidated by the job of cleaning the carbs – there is nothing to be worried about and I guarantee that a clean set of carbs will always outperform a neglected set. 

This cleaning method may not be the method of choice for others, but I have had excellent success using this technique.

So here we go – this is how I clean my R6 carbs - click on the highlighted words for descriptive photos. 

1. Wash the car and wash the exterior of the carburetors.  Make sure to plug the air filter inlets or use a ‘Scrub Bag’ over your filter(s).
2. Remove carbs from engine.
3. Remove air filters and any breathers from carbs.
4. Remove float bowls.
5. Remove screw holding the float pivot rod.
6. Remove float assembly.
7. Slide inlet needle off of float assembly.
8. Remove main jet holder assembly (using 8mm socket or wrench).
1. If your carbs have the emulsion tubes intact – remove emulsion tubes from main jet holder.
9. Remove pilot jet.
10. Tighten fuel screw while COUNTING the number of revolutions it takes until snug – write this number of revolutions down!
11. Remove fuel screws.
1. The fuel screws should have a rubber o-ring and a washer installed.  If you remove the fuel screw and there is no washer or o-ring, then they have remained in the hole.  You need to remove them or you run the risk of loosing them when you clean the main carburetor bodies!!
2. Use a small pick to (do not damage the o-ring) to remove the o-ring and washer.
3. Install the o-ring and washer on the fuel screw.
12. Turn the carburetors over and remove the vacuum slide covers and slide springs.
13. Remove the vacuum slides.  The vacuum slide diaphragms have a small brass insert installed --- DO NOT LOOSE THESE INSERTS!
14. Put the carburetors into a five gallon bucket with the throttle position sensor towards the TOP of the bucket.
15. Fill bucket with water and dishwashing soap until all four carburetors are submerged, but the throttle position sensor remains OUTSIDE the water.
16. Let the carbs soak.
17. Clean the slide assemblies:
1. Remove the slide needle clips.
2. Remove the slide needle – some carbs will have washers, o-rings or both installed on the slide needles – these are tuning aids, so make note where these are located on the needle.
3. Inspect slide needles for damage (bends, nicks, etc…)
4. Wipe clean the slides, diaphragms and retainer clips – use soapy water or WD40 – DO NOT USE CARBURETOR CLEANER!
5. Reassemble the slide assembly.
6. Inspect the small brass insert installed in the diaphragm.  There is a small hole in the center the insert – poke a cleaning rod through the hole.
18. Clean the floats, jets and needles:
1. Clean the main hole in main jet circuit and pilot jet.
2. Using small cleaning rods, poke EACH cross hole of the pilot jet and emulsion tube to verify they are clear.
3. Wipe clean the floats – be careful not to bend the floats or the metal inlet needle mount.
4. Inspect the inlet needles:
• The needles should be clean and corrosion free.
• The rubber tip should be intact with NO damage.
• The small button on top should move in and out smoothly.
5. Inspect the fuel screws:
• O-rings should be clean with NO damage.
• Washer should be present and installed between o-ring and screw.
• Tip of screw should be STRAIGHT.
19. Clean float bowls:
1. Be careful to not damage the float bowl rubber seal.
2. Use a stiff brush with soapy water, WD40 or carb cleaner to remove any material that has gotten down in the float bowl crevices – get it ALL out or you run the risk of clogging your carbs during a race.
20.  Remove carburetor bodies from soapy water.
21. Inspect carb bodies for dirt – clean with toothbrush as needed.
22. Dump soapy water from bucket.
23. Rinse bucket (clean the bucket).
24. Fill bucket with CLEAN (no soap) water.
25. Rinse carb bodies in bucket by agitating (move carbs up and down in water).
26. Remove carb bodies from water.
27. Blow dry carb bodies (60psi compressed air) – be sure to blow out the following holes:
1. Main jet circuit.
2. Pilot jet circuit.
3. Fuel screw hole.
4. Fuel inlet seats - blow into the seats from the seat side (opposite direction of fuel flow).  This will backflush the fine meshed screen that is installed under the inlet seat – THIS IS CRITICAL!!!!
5. Blow into the slide diaphragm holes.
28. Assemble the carburetors (jet side):
1. Install fuel screws (with o-ring and washer).
• Tighten fuel screws to snug.
• Loosen fuel screws the proper number of turns (remember, you recorded the number of turns out).
2. Install pilot jets (SNUG – do not overtighten).
3. Install main jet circuit (SNUG – do not overtighten).
4. Slide inlet needles into position on floats.
5. Install inlet needle into inlet seat while installing float.
6. Install float pivot screw (SNUG – do not overtighten).
7. Install float bowls.
29. Assemble the carburetors (slide side):
1. Lubricate the slides.
• Use a gun oil (I use ‘Outers’ brand Teflon multi lube) and massage the oil onto the slide surface.  This lube is important to keep the slides from sticking – I used to stick slides, but I eliminated that problem with this lube!
2. Install slides into carburetor bodies – do not force the slides – if resistance is felt you probably do not have the slide needle lined up with the main jet circuit in the throat of the carburetors – remove and try again.
3.  Seat the top of the slide diaphragm into the groove of the carb body. 
4. Verify the small brass insert is present in the slide diaphragm and in install it into small hole in carb body.
5. Install slide spring.
6. While keeping the slide diaphragm properly seated in the groove, install the slide cap.
7. SNUG the slide cap screws – verify that the diaphragm and cap are properly seated – if you have ANY doubt about the diaphragm being properly seated – remove the slide cap and try again.
8. Verify the slides operate freely and do not jam or stick.

Congratulations – you have an optimized set of Yamaha carburetors ready for the next night of racing.

Be sure to FLUSH methanol out of the carbs at the end of race night and keep your fuel filter(s) clean.