The TM28-418 is supplied with the following factory jetting installed:
Pilot jet 15 (VM22/210), Needle 5DP39, Needle Jet P-8 (175 Series), Main Jet 180 (4/042), Air Jet none, Slide 2.5 (832-33001)
Dimension A= 33mm, B= 82mm, C= 135mm, D= 44mm, Total Width 76mm
Unlike many motorcycle manufacturers’ purpose modified versions, these factory TM 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.
Mikuni’s (flat slide) carburetor, the TM Series Carburettors provide significant performance improvements over older round slide carburetors. Air flows faster and smoother through the TM Series venturi due to the flat slide design and the jet blocks which help create smooth bore effect.The high velocity of the air flow means a stronger vacuum at the needle jet providing more precise metering and better throttle response.
Performance features for the Mikuni TM Series Carburetors include a large selection of bore sizes for increased fuel mixture flow to match engine modifications. And the TM 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 TM28-418, 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 175 series needle jets (emulsion tubes) are limited 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 if the needle jets available dont fit the requirement will be to either linish your needle in the required area if too lean or if rich, research our 5 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 TM28’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.
(The picture with the cable shows the required length of inner cable protrusion and securing fitting at the carb end on basically a minimum length adjustment. The back board is divided into 1 and 10mm increments)