The new carbs and carb rubber thread

[Captain Chaos]

In the old thread about carb rubbers there was quite some incorrect info. The good man @Josephoffered to write a list with known correct information, from first hand, not hearsay. So here we go:

 

Carburetor guide to OC Suzuki bikes 

Collated by carburetor model, application and dimensions + info on swapping over and the use of Mikuni RS items.

All this info is taken from carburetors i have been able to check or fitments i have done.

 

VM29SS

Factory "racing" flatslide carburetors. Standard fitment for GSXR 750 85 to 87

Stub OD : 40
Airbox OD : 50

Same exterior dimensions as BST34, they can be swapped over plug and play.

Apparently it has also been common practice to overbore the 29s to 32-33mm

 

BST34

Standard fitment on GSXR 1100 1986-1988 and GSXF 1100 all years

Stub OD : 40
Airbox OD : 50

These swap over plug and play on the GSXR 750 85-87

 

BST36

Most used carburetors throughout the OC range

Standard fitment on Bandit 1200 (mk1), GSXR 750 1988-89, GSXR 1100 1989-90, GSXF 750 1988-1998 (mk1) GSX1100G all years

Stub OD : 42
Airbox OD : "Ovaled" shape > 58 width, 63 height

 

BST38

Only used two years on the GSXR 750 1990-1991

Stub OD : 46
Airbox OD : 58

They are give or take underbored BST40s, they swap over plug and play on GSXR 1100 1991-92 

 

BST40

Standard fitment on GSXR 1100 1991-92

Stub OD : 46
Airbox OD : 58

Swap over plug and play on GSXR 750 1990-91

 

 

Mikuni RS carburetors

They are sold with a 77-93-77 spacing, bear that in mind when it comes to fitting them on, because GSXR etc carburetors have a 78-90-78 spacing, requiring some massaging to slip them on, to, preferably, new inlets when available

 

RS34 

Stub OD : 40
Airbox OD : 55

(Note that they are also available with a 42mm stub OD)

The 40 OD will go on BST34 bikes/inlets

The 42 OD will go on BST36 bikes/inlets 

 

RS36 - RS38

These both have the exact same exterior dimensions 

Stub OD : 42
Airbox OD : 55

They share the same stub dimension as BST36 carburetors

 

RS40

Stub OD : 45
Airbox OD : 55

Slightly smaller than the BST40 carburetors, your only way to fit them is by using BST38-40 inlets and giving them a bit more tightness with the clamps

 

For all RS :

Sleeves are available to fit to the airbox side of the RS carburetors, to reach 58mm for oem fitment to enable airbox fitment where applicable.

To break it down :

RS 34 can fit BST34 bikes/inlets (or BST36 bikes if using the ones with a 42mm stub)

RS36 and 38 fit any bikes/inlets using BST36

RS40 only fit bikes/inlets using BST38 or BST40

 

 

Inlet rubbers - general info

It is always best to use new items, or renew them (although most are no longer available as we speak) 

They harden up over time and with fuel contact, and will have a tendency to shrink.

When new, they are approximately 1mm smaller in ID than the carburetors they fit, for obvious reasons.

It is best when storing unused inlet sets to leave them fitted to a matching rack of carburetors

 

 

GSXR WC carburetor conversion 

Oil cooled engines have a carburetor spacing of 78-90-78

WC engines have a carburetor spacing of 85-90-85

The GSXR 750 WC uses BST38 carburetors which is interesting for OC bikes.

The spacing being different compared to oil cooled engines, this mix can make them compatible in order to fit OC heads :

Spacing between cylinder 2 and 3 is the same, so just use the WC inlets
In order to make up for the difference in spacing on the outer carburetors, if you use an inlet nº3 on cylinder 1, and an inlet nº2 on cylinder 4, you'll almost catch up the right distances and the WC carburetors will go on.

 

 

Specials :

Bandit 1200 mk2 use BSR36 carburetors with a different spacing to the other OC engines, you would need to swap over the specific inlets with the carburetors for them to fit anything else

The GSXF 750 mk2 use BST36SS carburetors, they have the same spacing as mk1 and OC engines, and same 42mm stub as the BST36, but they have 58mm round stubs on the inlet side, making them ideal for pods/turbo applications 

 

Edited August 31 by Captain Chaos

[Gixer1460]

Quote

Standard fitment on Bandit 1200 (mk1), GSXR 750 1988-89, GSXR 1100 1989, GSXF 750 1988-1998 (mk1) GSX1100G all years

GSXR 1100 1989 AND 1990! 

[Swiss Toni]

Nice one @Joseph!

[Captain Chaos]

2 hours ago, Gixer1460 said:

GSXR 1100 1989 AND 1990! 

edited

[gsx]

That's good info

[bunk]

Are there any new carb rubber suppliers that work? Ive heard chinese rubbers are not worthwhile, what exactly is wrong with them and is it possible to tune them up to work? 

[DAZ]

Thanks for the update and the measurements  , in the specials section did you mean the mk2 gsxf750 has bsr36ss carbs spaced as the bst ( earlier o/c )  type ? As every thing I've read says post 98 teapot750 are bsr 

[Upshotknothole]

3 hours ago, bunk said:

Are there any new carb rubber suppliers that work? Ive heard chinese rubbers are not worthwhile, what exactly is wrong with them and is it possible to tune them up to work? 

They're not a full set, should be 4 unique intakes, instead they give you two of the same left and two of the same right intakes.

[bluecatone]

I'm modifying a chart that I found here, I'm not sure if info are correct, I just added the yellow highlighted section. Please help to fill empty spaces and correct mistakes.

[Upshotknothole]

19 minutes ago, bluecatone said:

I'm modifying a chart that I found here, I'm not sure if info are correct, I just added the yellow highlighted section. Please help to fill empty spaces and correct mistakes.

Only some markets got the BST40s on the GSXR 1100s. Here in the states and parts of Europe they came with BST36s, those intakes are the same as the MK1 Bandit 1200s and will also fit RS36/38 carbs. The 88/89 GSXR 750 rubbers which ideal for RS36/38s have been discontinued for a long time. They're also the same part that came on the MK1 GSXF750s, but unless you can find some NOS somewhere, they're most likely hard and cracked now.

The Bandit and GSXF 600s don't really interchange with anything and are best ignored. Early GSXF750s had dot heads and intakes, later have long stroke heads.

Might help to add a column for which ones are still available from Suzuki, as most of the ones in yellow I don't think are anymore. Also every model will have 4 different part numbers, a lot of those only have the first one listed.

Not sure on the sizing for Keihin carbs, and I think only WC versions are available to buy now. Haven't seen any new ones for OC spacing in years.

[Metralla]

Although slightly off topic...
What are the differences between J carburettors? West Germany (E22), Austria (E39) and Switzerland (E 18) have different P/N for the carb bodies.

[Upshotknothole]

7 minutes ago, Metralla said:

Although slightly off topic...
What are the differences between J carburettors? West Germany (E22), Austria (E39) and Switzerland (E 18) have different P/N for the carb bodies.

Different markets had different emissions and regulations and got different carbs or tuning. Factory service manual usually shows which models got full power and which ones were restricted.

[Metralla]

I know that, but being in restoration mode, I need to know If I can salvage eg E22 carbs or they are hopeless. What I try to understrand and please If anyone has an insight please let me know, is If the body/casting or the plastic sleeve inside have a restriction.

[Upshotknothole]

4 minutes ago, Metralla said:

I know that, but being in restoration mode, I need to know If I can salvage eg E22 carbs or they are hopeless. What I try to understrand and please If anyone has an insight please let me know, is If the body/casting or the plastic sleeve inside have a restriction.

Start a new thread so this thread doesn't get too distracting with random posts, and you'll get more people seeing your question. Later today I'll dig out my GSXR 750 factory manual and see if it has the info in it.