Mikuni: HSR42/45/48 High Performance Carburetors for Harley-Davidson motors

Go To: Data Sheet & Exploded View (downloads PDF file, .9mb) 

Details & Application Notes:

Mikuni's new HSR48 is a special version of the proven HSR42 carburetor. 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, airflow through an engine can be enhanced or limited by anything it must pass through. A restrictive air cleaner assembly, a too small carburetor, 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 airflow to highly developed engines.

Modified Harley or Harley-based engines tend to fall into one of three categories:

1)	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 carburetor.
2)	Highly modified --- A hotter cam, professional cylinder head port work, a more specialized exhaust system, high compression pistons and (Please!) a Mikuni HSR45 carburetor.
3)	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 modified 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. We do not make special manifolds for engines with non-standard cylinder head spacing or larger diameter intake ports. However, our HSR48 kit includes our rubber flange adapter that fits the S&S "G" series manifolds.

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.
Airflow:

The stock Harley CV40 carburetor 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 Harley: 185 CFM
Mikuni HSR42: 213 CFM
Mikuni HSR45: 237 CFM
Mikuni HSR48: 270 CFM

If carburetor airflow were the only factor, the HSR48 could deliver almost 50% more power than the stock carburetor. It isn't, of course, but a 50% gain could not be realized without a high flow carburetor.

In fact, one of our test "48's" was fitted to "Fireman" John Kownacki's 113" Evo-based 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 your favorite dealer. The "48" is available from all the usual sources.