More Information about the TM42 from MikuniOz:
"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 a sufficient starting point where alternating between WOT runs with and without the filter access door removed will confirm if you have removed enough material. The kit also comes with throttle cables and a 1/4 turn quick action throttle. The carb comes fully re-jetted for your application with spare main jets for fine tuning. 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 fitted what we have found to be a range of jets to allow you to tune to most variables. Though the TM42-6 will accept OEM choke cables, included in the kit is the optional knob choke assembly.
Fine tuning is generally related to exhaust system with the DR650 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 often pump nozzle. 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: (From MikuniOz)
"In the late 80’s Mikuni America 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 carburetors. 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."