1.Honda NX650 Mikuni TM42 Flatslide Pumper Carb KIT

(1 customer review)

$715.00 AUD$735.00 AUD

Please read the product description as some variations may apply.

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Please confirm your carb dimensions as some times a mix and match of engine mounting flanges as shown in the picture library and or other changes may require us to built with different diameter and length sleeves. 

Your carb should measure as per the picture A= 49mm, B= 100mm, D=62mm, please contact us if at all different. Using the shorter engine mount flange may work better with this application, where if changing over from the longer you will need to advise us so we can install a longer air box adapter onto the carb to compensate for the new required carb length difference. This may though not be sufficient for airbox connection with out a rubber boot change or using a POD filter.

This kit includes a Mikuni HSR 42mm Carburetor, where on most NX there is a frame down tube clearance issue with the carbs cable bracket requiring the frame to be modified along with some material removed from the cable bracket itself. The red frame pictures has had the area removed and boxed out out by the customer where preferably heat and compress the frame as done by the customer with the black frame (using the shorter engine mount flange). The inconvenience of these modifications is far outweighed by the improvement in performance. These Mikuni carburetors come fitted with silver anodized adapter sleeves to enable easy fitment to your Honda NX650, the stock rubber snorkel clamps down onto the slightly smaller inlet sleeve and the engine end is a perfect match to your 49mm outlet diameter. The kit also comes with throttle cables and a 1/4 turn quick action throttle which must be lubed before fitment and an option of a knob or short choke cable with universal mounting bracket. The carb has some Honda NX specific adjustments made and is pre-jetted for your engine. A specially made size 30 pump nozzle is fitted as the accelerator pump circuit on the TM42’s will not work properly on Honda’s without it. For this Mikuni carburetor to operate correctly the motorcycles air box must be opened up to allow more air flow in. Using a hole saw, a 45mm diameter hole will be sufficient for a Suzuki DR650 but some Hondas require way more. The best process is to keep opening up the air-box until no more improvement is noticed and you will be surprised at the difference. 

The Mikuni TM42-6 HSR flows 17CFM more than our TM40-6 and incorporates many upgraded features such as a roller-bearing slide. All this when compared to you stock carb means going even faster has never been so easy, say goodbye to hard starting, hesitations and flat spots.  

Climate, altitude and fuel density from different octane fuels all have varying effects on final fine tuning as does cam, exhaust and cylinder head porting etc. For this reason, we have included what we have found to be a range of jets to allow you to tune to most variables. International buyers please advise us of your fuel octane rating so we can make any applicable changes. Australian fuel is 91, 95 and 98 octane rated.

The TM42-6 for Honda applications comes with a knob choke located on the right hand side of the carb above the outlet spigot. This may be hard to get to or not be able to be fully engaged with some large capacity tanks where when ordering you can have the carb supplied with either the knob type choke or a cable and universal mounting bracket.

Fine tuning is generally related to cam or sometimes exhaust system with the XR where the supplied setup is in most cases perfect but if you don’t get that instant “WOW I’ve got myself a crazy wheel standing machine” feeling,  it will only usually relate to main jet size and or needle clip position setting. If at all confused or in need of guidance, we offer our customers business hours phone support for any carb we sell. The TM42 for big Jap singles are now our most popular selling kits worldwide and our knowledge base for tuning to different engine configurations of all brands is extensive.

You will instantly experience way better throttle response, improved smooth acceleration, increased horsepower and torque.  Plus the bonus of better fuel economy. Dyno tests show improvements of up to and over 25% when fitted to OEM carburetored engines. To fully appreciate the potential this carburetor has you must fully read and follow the provided fitment and tuning sheets.

To clarify some commonly asked questions about this carb in regards to a comparision with the 40mm: 

In the late 80’s Mikuni American released the HS40 (TM40-6) as an amazing new carburetor for the Harley Davidson market, literally knocking all its competitors out of the park. We were at the San Jose Custom Chrome Show when it was released and become part of that buzz as Australian Mikuni distributor. This slide type fuel metering device basically made the competitors butterfly type carbs seem like lawn sprinklers.
With the huge increase in Harley Davidson sales this became a very lucrative market. Recognizing the potential of this market and being aware of the efforts of competitors to try and grab back their share of it made Mikuni realize the necessity of replacing the 40 with a carburetor to be the be all and end all of all carburettors. The target was to deliver unrivaled peak performance combined with smoother throttle operation and lighter throttle pull by replacing the metal on metal slide action with a slide running on roller bearings. Also a larger fuel bowl capacity was provided but most of all, superior venturi design and fuel atomization resulting in more precise mixture ratios to not only increased horsepower and torque but also to enable the fitment of a larger carb to smaller capacity engines without losing valuable bottom end power, where in fact instead gaining more. In 1994 the HSR42 was born and just like you will if you fit one to your bike, all we could say was WOW. Instant throttle response delivering 25% more horsepower and torque over the stock CV carb before even putting on a real high flow air-cleaner. As the badge says 20 years later” Still the best performance carburetor on the planet”.
Unfortunately, the TM42 only had limited sales in the Japanese single market due to it only appealing to the custom fitter as there had never been a cable set or air-box adapter available off the shelf. With the slowing of the Harley market due to fuel injection on new bikes, here in Australia, Mikunioz realized the opportunity to offer Mikuni’s best Carburetor to the big Jap single market and in late 2015 we released a range of ready to roar direct fit up kits with correct jetting and a few trick mods to make them work better than anything before on big Jap Thumpers.

The fuel consumption is way less but when comparing with the stock carbs, it all depends on how having a lot more power and torque effects your riding habits. If you can manage to back off and just have your bike perform at its present level you’ll be surprised by the fuel economy, but of course when the same amount of throttle twist becomes front wheel lifting, breaking traction action, well it’s hard to not want to go and play. If you have more horses in the paddock and you want them all to perform, you have to feed them more hay! 

You will enjoy this new carb but do be sure to hold on tight on your first test ride as she may try to spit you off if you nail it to hard.


If wishing to modify or depress your frame so as to use the standard form TM42 which usually has frame clearance issues with the RH cable bracket or use and modify your existing Honda XR600, XR650 or NX650 cables to suit the Mikuni TM42-6 or use a POD filter rather than the original air-box you can purchase the carburetor, tuner jet kit and or what ever other components you want individually by following the directions below.

On the main menu to the left of the page, hover over the carb listing for TM Carbs with Accel Pump and then select TM42-6 from the drop down list. When clicking on any individual size Mikuni carb from the drop down list it will put you into a page showing not only the Mikuni carb itself but also any items relevant to that carb, being Mikuni jets, Mikuni flanges, Mikuni carb tuner kits, Mikuni cables , Mikuni throttles, Mikuni air-cleaners and a range of Mikuni carb to OEM air box adaptors etc to also suit. This also makes alternate jet selection easy for you if you have your own spec as only the type jets for that particular carb are shown.
Click on the carb itself if wanting to view the full details and or to make your purchase. Then back arrow back in the carbs main page and go into the tuner kits, which show in the sales drop down list the jetting kits we have for confirmed suitable engines for that particular carb. Again thoroughly read the tuner kit description.
If you’re comfortable with making a purchase of the carb, tuner kit any or other associated components, order it on line or otherwise please call us to further discuss your needs on 0747712677.

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.

Additional information

Select Choke Preference

Knob Choke, Cable Choke w. Bracket

1 review for 1.Honda NX650 Mikuni TM42 Flatslide Pumper Carb KIT

  1. Adrian Chaloner (verified owner)

    This Carby is a Game Changer i have a 93 RD02 NX650 and the moment on the wrist is so worth it Tom is Awesome and will support you with what you want to achieve. I recently fitted a 2 into 1 Arrow single stainless exhaust and fitted a wide band O2 sensor and gauge opened up my airbox completely running a Unifilter 150mm Foam Oil Filter and it has totally allowed me to dial in that sweet spot and have just got it good, I’m running the Leaner Needle jet (98) one clip above centre with a 150 Main Jet and a 30 Idle jet exactly 1.5 turns out from bottom and averaging around 12 to 13 AFR

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