The Mikuni VM20-273 is supplied with the following factory jetting installed:
Pilot jet 22.5 (M28/1001), Needle 4J13, Needle Jet O-6/N-6 (238/332 Series), Main Jet 180 (4/042), Air Jet 0.5, Slide Cutaway 2.0 (VM38/24), Needle valve 1.5 (VM15/172)
Mikuni VM20-273 Dimension A= 50.8mm Bolt Centres, B= 66mm, C= 115mm, D= 43mm, Total Width 76.5mm
Unlike many motorcycle manufacturers’ purpose modified versions, these factory VM Round Slides are both 2 and 4 stroke compatible and are regarded by the factory to be the best performing version of this carburetor ever made.
These are the most popular high performance singles carburetors in the sport of motorcycling. Mikuni’s VM Series round slide single carburetors have proven themselves as the performance standard for use in any single cylinder motorcycle and ATV applications for motocross, enduro and trail riding, to flat track racing and road racing on both 2-stroke and 4-stroke engines.
Performance features for the Mikuni VM Series Carburetors include a large selection of bore sizes for increased fuel mixture flow to match engine modifications. And the Mikuni VM Series offers a wide range of tuning components to allow precise fuel mixture metering in any application, at any throttle setting, under any riding conditions.
Tuner jet kits can be purchased separately for many different motorcycles as per the corresponding options. These kits consist of the suggested jets for changing that are not matching those factory fitted in the Mikuni VM20-273, they include an extra one size up and one size down main jet for tuning the main circuit due to fuel quality variations, altitude and climate. Testing and conformation of correct main circuit jetting can only be done by physically changing jets and WOT testing.
Warning: Richer or leaner needle jets (emulsion tubes) are not available for this carb and you need to be aware that when trying to adapt this carb to an unfamiliar engine that it may be untunable if the mid-range jetting needs changing after raising or lowering the needle to its limit The only option in this situation will be to either linish your needle in the required area if too lean or if rich, research our 4 series needles listing with a view to trying or modifying one. This is a common practice for racers and race tuners but do be aware if not in your field of expertise we do not take returns, so for us it’s better to pre-warn you and not have a complaining customer later rather than to mislead you. Be very careful of sellers telling you otherwise unless you’ve done your home work in regards to this carb being a suitable and tunable upgrade or replacement for your engine.
These tuner jet sets have been determined from thirty years of experience, customer feedback, plus research and development as the Australian Mikuni distributor. From time to time these may not be exactly right for every engine, usually due to changes to porting, compression or numerous other things that contribute to the requirement for additional fine tuning but as a rule our kits are spot on or a very close and useful starting point, but we give no guarantees and sorry do not release kit details or jet size information. If you have your own spec simply purchase the carb and buy any other required jets from the jet pages. This also applies to replacing jets in other Mikuni VM20’s as some items may not match and fit.
Keep in mind that these are suggested specs, and all tuning procedures, as found in our Tuning Tips section must be adhered to for the confirmation of any supplied jet’s compatibility with your engine.
All international buyers are responsible for the payment of their domestic customs duties and taxes charged on imported goods. The duty free threshold and duty/taxes payable rates differ from one country to another and we strongly advise you check your liability before ordering if unsure. Please check your tracking on all international shipments within 7 days to follow their progress and determine if it is being held by your local customs dept. or on their behalf by the Postal Service, who you will need to make contact with using the provided tracking number.
Please Note: Other than exact replacement OEM carburetors, all Mikuni Aftermarket Carburetors and Tuning Components are sold “As Is” for Off Road / Racing Use Only and are not intended or approved for use on vehicles operated on Public Roads or in locations where applicable engine tampering and anti-pollution laws apply.