Mikuni HSR42,45 and 48 Carburettors
*Note: The new HSR48, based on the HSR42, has been designed
for applications requiring extreme power. Click for
details below.
Going fast has never been so easy. The number one performance
carburettor now slips onto your Harley using the original throttle cables.
Mikuni's Big Twin and Sportster/Buell Easy Kits even use your bike's
existing manifold, choke cable and air filter. Keep your Harley's stock
factory look and fit, with better throttle response, improved
acceleration, increased power and torque. Mikuni's smoothbore, flatslide
with roller bearings, and accelerator pump technology delivers peak
performance from idle to Wide Open Throttle.
These carburettors are for all Harley Davidson owners and are available in
standard aluminium finish or the chrome and polished version.
NOTE: Choke cable is included except in the TM42-6, which will use
stock cable from CV type carb.
| TM42-6 |
HSR 42 mm Carb. |
Standard finish |
| TM42-6P |
HSR 42 mm Carb. |
Polished finish |
| TM45-2 |
HSR 42 mm Carb. |
Standard finish |
| TM45-2P |
HSR 42 mm Carb. |
Polished finish |
The Newly Available HSR48
HSR48 Details and Applications
Mikuni's new HSR48 is a special version of the
proven HSR42 carburettor. Its purpose is to provide maximum airflow for
the most demanding high performance engines.
The amount of power any engine can
deliver is directly related to the volume of air it can use in a given
time together with its efficiency in using that air. Everything else being
equal, more air equals more power.
Leaving port and combustion chamber design aside, air
flow through an engine can be enhanced or limited by anything it must pass
through. A restrictive air cleaner assembly, too small carburettor,
restrictive intake manifold and a restrictive or poorly designed exhaust
system can (each or all) limit power output. The HSR48 was developed
to
deliver additional air flow to highly developed engines.
Modified Harley or Harley-based engines
tend to fall into one of three categories:
-
Modified stock --- This engine typically has
stock cylinder heads, a high flow air cleaner, high flow mufflers,
perhaps a bolt-in cam and (Hopefully!) a Mikuni HSR42 carburettor.
-
Highly modified --- A hotter cam, professional
cylinder head port work, a more specialized exhaust system, high
compression pistons and (Please!) a Mikuni HSR45 carburettor.
-
All-out ground pounder --- Highly modified
heads, a displacement increase, either by way of fitting larger
pistons, a stroker kit or both. This engine is more likely to be a
special engine, built from the ground up to be stronger and to process
more air than even a highly modifed Harley motor. This is the
sort of motor that should have the HSR48.
There is little to be gained
from installing the HSR48 on an engine with stock cylinder heads or one
that is going to be fitted with an exhaust system more suited to looking
good than passing gas. The number of bolt-on performance options becomes
very narrow when one attempts to get their engine above 100 (or so)
Horsepower. We advise that you carefully consider the suitability of other
performance components when you consider installing the new HSR48.
Our HSR48 is slightly larger than
either the HSR42 or the HSR45. It is taller and the spigot (engine side)
is larger in diameter. This may result, with some installations, in
interference problems with chassis parts. While Mikuni does have a
manifold assembly that fits the "48" to a stock Evo or Twin Cam motor, we
do not make special manifolds for engines with non-standard cylinder head
spacing or larger diameter intake ports. The large variation in "Ground
Pounder" engine configurations together with the relatively small number
of such engines limits Mikuni's ability to produce special manifolds. You
may need to cut some metal.
Air Flow:
The stock Harley carburettor flows about 185 CFM
(cubic feet per minute) when flow is measured at a pressure difference of
12-inches of water. All the Mikuni HSR-series flow considerably more:
Stock: 185 CFM
HSR42: 213 CFM
HSR45: 237 CFM
HSR48: 270 CFM
If carburettor air flow were the only factor, the HSR48
could deliver almost 50% more power than the stock carburettor. It isn't,
of course, but a 50% gain could not be realized without a high flow
carburettor.
In fact one of our test "48s" was fitted to "Fireman"
John Kownacki's 113" motor with which he then recorded 156 Horsepower on a
Dynojet 150 Dyno. This is a streetable engine and Mr. Kownacki prides
himself on the fact that he rides it nearly every day.
If you think your motor is a candidate
for an HSR48, contact T.D. Hatrick & Co. (details below).
