How To Identify The Mikuni Carburetor In Your Motorcycle

Table of Contents:

I. Introduction
II. Mikuni Carburetor Identification
[1] How to know your Mikuni carb is fake or original?
[2] How to identify Mikuni carb size?
[3] How to know which Mikuni carb you have? How to find the carburetor number?
[4] HSR Series Carburetors: 42, 45 and 48 mm smoothbore carburetors
[5] RS Series Carburetors
[6] Mikuni TMX/TMS Series Carburetors
[7] Mikuni TM Series Carburetors
[8] Mikuni VM series carburetors
III. Is Mikuni a good carburetor?
IV. Conclusion

I. Introduction

If you own an old model motorcycle and you do not have the user manual, there are chances that you will have difficulty identifying the parts, including the carburetor.

You only know that it is fitted with a Mikuni carburetor and you want to know its code and size and whether it’s a genuine Mikuni carburetor?

II. Mikuni Carburetor Identification

In this section, we will try to find the answers to the following questions:

  • How to know if your Mikuni carb is fake or original?
  • How to know which Mikuni carb you have?
  • How to identify Mikuni carb size?
  • How to find the carburetor number?

[1] How to know your Mikuni carb is fake or original?

Original or genuine Mikuni carburetors have a body of aluminum alloy die casting and you can see the markings ‘MIKUNI CORP’ and ‘MADE IN JAPAN’ very prominently on the body (the markings are cast into the body).

If you have seen and handled a Mikuni carburetor earlier, you’ll be easily able to differentiate the original from the fake by just taking the carburetor in your hand; one clear cue can be that the fake one will be much lighter (otherwise, how can they be priced low).

Our next question is how to identify your Mikuni carburetor in terms of its size and code.

For this, you need to take out your carb from your motorcycle and clean and dry it. You can do this yourself if you have previous experience of handling carburetors or take the help of your mechanic.

[2] How to identify Mikuni carb size?

In the code or designation of a Mikuni carburetor like HSR 42 or TM 42, HSR or TM indicates the design of the carburetor and 42 indicates the bore (internal diameter) size (in mm) on the engine end of the carburetor (your carburetor has two ends, one end is connected to the engine (engine end) and the other end is connected to the air filter (air filter end)).

Examine the engine end of the carburetor and you may find the stamped marking like HSR 42 or similar to that which indicates the design and size of your carburetor.

If you do not find any marking or if the marking is faded (using a rough brush for cleaning the outside of the carburetor may wear out the markings), then you have to use a Vernier caliper or a good quality steel scale to measure the bore on the engine end in ‘mm’; this gives you the size of the carburetor.

[3] How to know which Mikuni carb you have? How to find the carburetor number?

I have collected the information of Mikuni single carburetors of all designs (used in motorcycles) and sizes and compiled them in Table-1 below. This information is collected from the Mikuni catalog.

You can download the Mikuni catalog at this page

As per the catalog:

  • HSR 42, TM 42-6, and TM 42-6PK are the same, except the finish on the body, and similarly, HSR 45, TM 45-2K, and TM 45-2 PK are the same except the finish on the body.
  • Also, Mikuni HS 40 and TM 40-6 are the same.

So after measuring the bore on the engine end, let us consider the following:

If the bore size is 48 mm, your carburetor number is HSR 48 since there is only one Mikuni carburetor with a 48 mm bore size (Table-1).

Similarly, if the bore size is 42 mm, you have Mikuni HSR 42 whereas a bore size of 45 mm indicates an HSR 45.

What if the bore size is 38 mm, your Mikuni can be TMX 38-27 or TMX 38-18 or TM 38-85 or TM 38-86 or VM 38.
Do not worry, take your caliper again and measure the dimensions A, B, C, and D to find the design code of your Mikuni. (Please see Table-2, Table-3, and Table-4 for the details).

TABLE-1

MIKUNI CARBURETOR SERIES AND CODE

HSR seriesHSR 42HSR 45HSR 48
TM seriesTM 42-6TM 42-6PKTM 45-2KTM 45-2PK
HS SeriesHS 40
TMX SeriesTMX 35-1TMX 38-27TMX 38-18
TM SeriesTM 24-8001VM 28-418TM 32-1TM 33-8012TM 34-2TM 36-2TM 36-68TM 38-85TM 38-
86
TM 40
-6
VM SeriesVM 18VM 20VM 22VM 24VM 26VM 30VM 32VM 34VM 36VM 38VM 44

(This information is compiled from the Mikuni Catalog)

The following paragraphs give you a brief introduction about the different designs of Mikuni carbs used in motorcycles.

[4] HSR Series Carburetors: 42, 45 and 48 mm smoothbore carburetors

Mikuni HSR Series carburetors are used in Harley-Davidsons and American Big Twins. The numbers 42, 45, and 48 indicate the bore size at the engine end, 42 mm, 45 mm, and 48 mm respectively.

HSR 48 is the preferred one for racing motorcycles. HSR series has flat-slide throttle with roller bearings and accelerator pump.

HSR and TM carburetors are the same for the following sizes.

TM 42-6 isHSR 42 mm carburetor with a standard finish.
TM42-6 PK isHSR 42 mm carburetor with polishing on the outside surfaces.
TM 45-2K isHSR 45 mm carburetor with a standard finish.
TM45-2 PK isHSR 45 mm carburetor with polishing on the outside surfaces.

[5] RS Series Carburetors

Mikuni RS Series carburetors are designed and built for in-line four-cylinder engines of performance motorcycles and come with radial flat slides for throttling. Mikuni RS series carburetors are available in sizes 34, 36, 38, and 40 mm.

Mikuni RS series carburetors have push-pull type throttle assembly to assure positive closing of the carburetor throttle slides for high-performance racing engines.

[6] Mikuni TMX/TMS Series Carburetors:

They are available in sizes 35 and 38 mm.

Mikuni TMX series carburetors use flat slide throttle in a smooth bore venturi.

TMX series carburetors of 35 mm bore size are used for 125 cc race engines whereas 38 mm bore size is used for 250 cc race engines.

Mikuni carburetors

TABLE-2
MODEL→TMX 35-1TMX 38-27TMX 38-18
DIMENSION↓
A404447
B76
C164
D62
Total width76

(This information is compiled from the Mikuni Catalog. All dimensions are in mm)

[7] Mikuni TM Series Carburetors

Mikuni TM Series carburetors have flat slide throttles and are available in sizes 24, 28, 32, 33, 34, 36, 38, and 40 mm.

Mikuni carburetors

TABLE-3
Model no→TM24-8001VM28 -418TM 32 -1TM33- 8012TM34- 2TM 36- 2TM 36- 68TM 38- 85TM 38- 86TM 40- 6
Dimensions↓
A31334040404342474344
B7582839383100100100100100
C145135160160160170176170170165
D44445850586254626255
Total width7676781057875787575

(This information is compiled from the Mikuni Catalog. All dimensions are in mm)

[8] Mikuni VM series carburetors: They have round slide throttle and are very popular for their application in the sport of motorcycling and ATV (All-terrain Vehicle). VM series carburettors come in sizes 18, 20, 22, 24, 26, 30, 32, 34, 36, 38 and 44.

Mikuni carburetors

TABLE-4
Model no→VM 18VM 20VM 22VM 24VM 26VM 30VM 32VM 34VM 36VM 38VM 44
Dimensions↓
AClamp-on 22 IDFlange 50.8 Bolt CTRFlange 49 Bolt CTR3535404352
B67668580939310293116
C108115114116122137142137152154193
D3243434344586270
Total width6176.58282828379

(This information is compiled from the Mikuni Catalog. All dimensions are in mm)

Mikuni has got Super BN series Carburetors specially designed for high horsepower racing watercraft.

III. Is Mikuni a good carburetor?

Mikuni carburetors are the products of Mikuni Corporation, Japan and they are in the field of carburetors and other automotive-related products for more than 60 years. They are well known and are one of the leading manufacturers in this field.

Mikuni American Corporation is a subsidiary company of its parent company in Japan and has its offices/works at Chicago and McAllen (Texas) (www.mikuni.com). This subsidiary was formed in 1968.

Mikuni Carburetors in ‘Aftermarket sales’ are sold for off-road and racing purposes only. However, there may be some Mikuni carburetors supplied as OEM (original equipment manufacturer) to motorcycle manufacturers for on-road and city use.

Mikuni Carburetors which are not designated as C.A.R.B. (California Air Resource Board) cannot be fitted on motorcycles that are intended to be used in towns or on freeways in the state of California and other states with similar restrictions on pollution control.

IV. Conclusion

Mikuni carburetors are mainly sold and used for off-road ATVs and racing purposes only. Because of this, Mikuni carbs should be replaced or repaired by the authorized dealer of Mikuni or by an experienced mechanic trained in Mikuni carburetors.

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3 Comments

  1. Robert M Ehlenbach September 27, 2020
  2. Robert M Ehlenbach September 27, 2020
  3. Jon Trygve Stokka March 12, 2021