1. TM38-27, 38mm TMX Mikuni 2 Stroke Racing Carb (44mm Spigot)

(3 customer reviews)

$250.00 AUD

or 4 fortnightly payments of $62.50 AUD with Afterpay More info

Out of stock


The TM38-27 is supplied with the following factory jetting installed:

Pilot jet 20 (VM22/210),  Needle 6EJ12-55 (richer and leaner available),  Needle Jet (Fixed in place),  Main Jet 370 (4/042),  Slide  3.5 (999-832-014)

Dimension A= 44mm, B= 76mm, C= 164mm, D= 62mm, Total Width= 76mm

Unlike many motorcycle manufacturers’ purpose built and modified pollution compliant versions of the TMX carb, these factory TMX flatslide racing carbs are regarded by the factory to be the best performing version of this carburetor ever made.

The TMX features a flat slide design in a smooth bore venturi to provide improved throttle response and wider powerband. The float system with independently moving floats, working with a main jet enclosed in a baffle chamber, allows the TMX to perform smoothly without hesitation on the roughest terrain. These carbs are jetted to suit virtually anything from later model 125cc high performance motocross engines, all 250cc reed valve motors and also all of the larger two stroke engines which perform great with often never a jet change. If fitting to a piston port engine, they do require a drastic jetting down size.  Once fitted it will eliminate a lot of the hesitation, hard starting and other performance problems experienced with some OEM carbs and best of all will boost performance..

It is always advised to buy a spare one size up (380) and one size down (360) main jet so as to positively verify your correct fuel mixture and optimum power at WOT. When replacing carbs with throttle position sensors and other such electrical items fitted you will need to determine if these do not need to be connected before purchasing and installing one of our carbs.

If your carb measures around 12mm, 20mm or 40mm longer than the 76mm front to back measurement of the TMX carb, and if intending to still use the standard air-box you will need to purchase separately from our TMX Carbs page the corresponding silver anodized extender. When ordering an extender with your carb please advise in the order comments section if you want us to press fit it to your carb with Loctite before delivery. The two shorter extenders have an outside diameter of 60mm at the air-box end which is slightly smaller than the carb itself and the 40mm long one is 62mm diameter.

The picture above with the cable shows the required length of inner cable protrusion and securing fitting required at the carb end at basically a minimum length adjustment. The back board is divided into 1 and 10mm increments. If your inner cable is to short you may consider one of our Quick Action throttle and cable assemblies.


The jets in this carb are spot on for most motorcycles with a few requiring a main jet changed as suggested above and once fitted and checking the pilot setting, occasionally some motors may ask for a one or two size leaner pilot where Husky’s often like a 25. The needles only ever may need a change when fitted to some multi cylinder applications. Follow the tuning sheets supplied with the carb and if requiring a change, the perfect tune is easily achieved.


The Jet Needle is the tapered rod that is positioned in the throttle valve by the ‘E’-Clip. The taper of the needle increases the clearance between the Jet Needle and the fixed Needle Jet outlet as the throttle is opened. As the air flow volume increases past the throttle slide, the fuel volume is also increased to maintain the correct air/fuel ratio.


The position of the ‘E’-Clip in the Jet Needle is used to correct or change the air/fuel ratio between 1/4th and 3/4th throttle valve position. The ‘E’-Clip can be raised or lowered on the Jet Needle. To richen the fuel mixture the ‘E’-Clip is lowered on the Jet Needle, raising the Jet Needle. To lean the fuel mixture the ‘E’-Clip is raised on the Jet Needle.


To correct the fuel mixture at 1/8th to 1/4th throttle slide position it may be necessary to change the Jet Needle. The Jet Needle will have a series of numbers stamped on it.
Example: 6EJ 12-55. The numbers 55 indicate that the outside diameter (O.D.) of the Jet Needle is 2.55mm. A smaller O.D. number gives a richer mixture. A larger O.D. number gives a leaner mixture. Typical Jet Needles available:

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.


3 reviews for 1. TM38-27, 38mm TMX Mikuni 2 Stroke Racing Carb (44mm Spigot)

  1. Doug

    Wow what an easy fix for all the issues I had with my OEM carb and more power to boot, many thanks for the prompt service and terrific product.

  2. Brenden Jones

    Hi, I would just like to leave some feed back on the 38mm TM flatside carbie that I purchased for my YZ 490 L.

    When i first got in contact with Tom about rebuilding the 38mm round as I wanted to keep it original???

    I was told that all my problems would be solved if I went with the 38mm TM Flatside. Did I listen… No.. I went for the rebuild and still had the same problems, bike wouldn’t start, then wouldn’t Idle, then it would start again then not start again.
    I replaced everything thinking it might be spark, an air leak etc etc.

    The motor was fully rebuilt new crank, cases milled flat, crank balanced complete rebuild.. still wouldn’t start and or keep starting.

    I rang Mikuni 3 months later explained what I had done and I got the answer “I told you so, put a 38mm TM Flatside on it.

    Weellll.. I did!! Booom Second kick with hardly any kick though. I have never had a problem since, Starts first kick , the power is smooth and right through the range, no changes it was perfect straight out of the box.

    I have just finished a YZ250 T and I am restoring a WR500 both will be getting a 38mm TM Flatside.

    Thanks guys

  3. John Padley (verified owner)

    I restored an unmodified 1989 YZ250W and replaced the stock (license built) Mikuni TMX with the genuine Mikuni TMX as recommended by Tom and it worked perfectly straight out of the bag. Don’t mess around trying to fix up old carbies, these new ones fit straight on and work perfectly.

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