• New carburetor diaphragms for the MIKUNI BS38 CV* Carburetor used on Yamaha 650 vertical twins. These are CV* ( constant velocity ) carbs used from 1970 till
    77 mm OD00000" size="2"> of diaphragm groove. Does NOT fit the carbs used from 1980 on. You must use BS34CV diaphragms ( 73 mm OD ) if your bike was made in 1980 till end
    of production.  Check your diaphragm groove diameter.
Cracked worn or torn diaphragms can allow imbalance to carburetors causing one cylinder to work harder than the other.

This diaphragm set does NOT include new throttle slides. This is a easily installed rubber part that goes on your old slide. The rubber is attached to the slide by pushing the thick
section over the swagged lip that held the plastic washers. The thick section of rubber grips the slide and replaces the plastic washers.  The pictures should explain how this
Please print these instructions.

A quick mail to say that the M-77 fit BS36's on an '83 Suzuki GR650 Tempter.

Your diaphragms work great. I have about 2K on these so far and so far so good. XS400
Regards,  Waldo

Rubber was nice. Almost to easy to install. Fit the grooves on slide and Carb body perfect. M-73  

Hi Don,
I just wanted to provide you some feedback on your products…they work great!  I installed them on my ‘81 Yamaha XS400 with BS34CV carbs.  They went on easy, and the bike
ran like new.  The bike went from almost non-running to tearing up the neighborhood in less than an hour.
Thanks for the great product and fast delivery,

Just wanted to say that I received the diaphragms and that they were absolutely great!
Allthough the old diaphragms didn't have any holes in them, replacement improved performance dramatically.
Best money I've spent in a long time, great value, thanks for making such a product available!
Best regards,
Oeyvind Elbert
Hagaveien 15b
1387 Asker

I just received the new BS38 diaphragms, and am extremely happy. Very nice work, and I can't thank you enough for saving the carbs on my 79 XS.
Thanks a million!
Norm McRae

Just to say diaphragms arrived on friday 21st, I fitted them today 22nd, they fitted perfectly and very straight forwardly. Ballanced carbs  , one very happy
FJ 1200. Regards
Graham...... Northumberland, England.

Great alternative to $300 NOS slides. Works as advertised.
Buyer: wch69sooner2010 ( 3 )  Apr-09-10  
YAMAHA XS, TX 650 Mikuni BS38 CV Carburetor Diaphragms (#230435468325)

As Usual...PERFECT!!!!
Buyer: spydercycleworks ( 3184)  Mar-31-10  
YAMAHA XS, TX 650 Mikuni BS38 CV Carburetor Diaphragms (#330413174303)

Super quick, great product and seller! Thanks Don
Buyer: bluebikerblan ( 57)  Mar-24-10  
Yamaha XS 650 Carburetor Holder Socket Boots USA made (#330411790711)

Item worked great and quick delivery very pleased
Buyer: gerald.423 ( 4 ) Sep-14-09
YAMAHA XS, TX 650 Mikuni BS38 CV Carburetor Diaphragms (#330355707704)

Thank you. Very cheap shipping A+ Good part at a super price wish I had got more
Buyer: jeremyb977 ( 26) Jul-09-09
YAMAHA XS, TX 650 Mikuni BS38 CV Carburetor Diaphragms (#230348064346)   

Worked like a charm. I wasn't sure if I'd ever be able to find this part again.
Buyer: shadowstep07 ( 20) Jun-22-09

What a great product. 15 mins to install, bike running like a dream again. A++++  
Buyer: izibead2012 ( 28)          Feb-16-13
YAMAHA Diaphragm SR250 XS650 XJ400 XJ1100 XJ900
Venture XS400 XV535 Mikuni BS34 ......Mikuni  BS34

Hello! These  M-73 diaphragms is just a awesome!!!Fit perfect to my Suzuki gsx 400e 1983.
Regards,  Tom,  Finland.   t.bergstrom@luukku.com

Nice parts-good service
Buyer: senpga ( 69) Jun-08-09
YAMAHA XS, TX 650 Mikuni BS38 CV Carburetor Diaphragms (#330333032461)

Quick and accurate
Buyer: joara172 ( 29) Jun-08-09
YAMAHA XS, TX 650 Mikuni BS38 CV Carburetor Diaphragms (#330333032461)

Awesome great part
Buyer: 970_anchondo ( 18) Sep-03-09
YAMAHA XS, TX 650 Mikuni BS38 CV Carburetor Diaphragms (#230359062132)

The parts fit and work perfectly
Buyer: Member id klaus_the_great   Nov-13-10
YAMAHA 650 Mikuni BS34 CV Carburetor Diaphragm, Suzuki (#230539666945)

Thanks for the very good service and perfectly parts.
besten dank für den tollen service die schnelle lieferung .
die membranen passen perfekt sehr gute einbauanleitung bin sehr zufrieden!!!
vielen dank aus deutschland.
sven spicker

Just wanted to say thanks ............
The diaphragms arrived yesterday, were put in today and I couldn't be happier with the results !!!
WOW !!!
Thank You !!!
John M. Wright
388 Painter Street
Rio Dell, CA. 95562-1432

I have just installed M-70 diaphragms on my Mikuni BS 33 carburetors from a  1985 Yamaha Maxim X XJ700XN. The parts fit perfectly, installed easily and operate
flawlessly. This diaphragm will also work on models XJ700XNC from 85' as well as the 86' models XJ700XS and XJ700XSC , (the only two years these models were
made as far as I know) so please add these to your list of bikes these diaphragms will fit as it may help some poor soul trying to locate these rare and hard to find parts...
or paying $180 per slide and diaphragm assembly (which there are four on these bikes). Thank you for an excellent part at a fair and honest price and prompt delivery
(2 days). I hope this helps someone find a part that they are looking for....Thanks again!   Randall Edwards

These diaphragms are easy to install and restore XS650 carbies BRILLIANTLY!!! Buyer: Member id laoshi50 ( Feedback Score Of 304)  Apr-12-11 03:20
TX 650 Mikuni BS38 Carburetor Diaphragm 77mm (#330543642298)

Test drive was awesome! Great diaphragms, huge performance difference! Thanks Buyer: Member id 1105sunnylake ( Feedback Score Of 1 )  Apr-22-11 06:52
Diaphragm KZ700/750/1000/1100 VS-750 MIKUNI BS34SS 70mm (#230598414002)

RE: XJ900F BS36CV ...-Thanks for the delivery. I installed the diaphragms and they work like a charm. My bike has full power again and is running great.
Regards, Henry.

Thanks for the BS34CV73mm diaphragms. I have fitted one to my Yamaha SR250SE 1981 and it works a treat, the old diaphragm had a total of 5 holes in it!
Richard Warner.

I purchased a pair of diaphragms for 35mm Mikuni s for my
1980 XS650 a while back,  which have been fantastic, not a problem.
I live in Newcastle, Australia

Quick message to let you know BS38 diaphragms fit
yamaha XS500 fitted with Mikuni BS38 CV carbs...fitted a treat.

Hi Don,
RE: XJ900F BS36CV  That was fast - I got the parts this morning & installed them
already. Work fine. Thanks for the fast service. Rgds, Chris.

the replacement Carburetor Diaphragm came it today.The quality of these parts is perfect and
better than the original in my opinion.
I am working on Motorcycles since 1979 and was happy to get these high quality spareparts.
Thank you very much for your kindful help and assistance and the fast delivery
Berlin/Germany WOLF......

Hi Don,
Thank you for your speedy reply. Payment sent via PayPal.
PS. I just returned from a 1,000 mile round trip after installing the new BS34 set I borrowed from a good friend and they performed excellently I was very pleased.
Ben Bennink

I need 4 BS34 diaphrams. These will fit the 1980 Yamaha XS1100 SG (Special)  that I'm rebuilding. Thank you for your time. -- Also the set I bought for my 1979 Yamaha XS1100
SF (special) work perfectly. Thank you for a great product.
Peter Albers

I now have used several of your Diaphragms for the CB360, CB350 and KZ440 I have found them easy to install and they work VERY WELL .

G'day Donald,
I received the diaphragms not this week, but last. I was waiting for my dad to pick them up and have a look as they are for his TX750. He is very happy with them. Your service has
been excellent and would not hesitate in dealing with you again.
Regards and best wishes,   Tony Oxenbridge.

* Constant velocity carburetors actuate the throttle slide and needle at anything over a fast idle. The atmospheric depression or vacuum caused by the venturi of the
cut-away is used to raise the slide by means of the vacuum on the top of the diaphragm. ( There is a communication hole to the venturi in the throttle slide.)
Made in USA on limited basis with high quality rubber.
Reasonable shipping worldwide!
Top and Bottom of diaphragms shows thick tire section.
Yamaha SX, TX650, TX750, Venture, & Kawasaki KZ-750, XS500 Carburetor Diaphragms
for Mikuni BS38, BS36,  BS34, BS34SS, & BS32 CV
constant velocity carburetors. This
easy to install part can cure engine stuttering, unwanted acceleration, uneven and
unbalanced carburetors caused by leaking or worn diaphragms.
You must cut the plastic rings on the slide to install.
This pair of Yamaha 650  or KZ 750 carburetor
diaphragms fits Mikuni BS38 CV constant velocity
carbs. Easy and inexpensive fix & made from
aircraft quality rubber so they will last.
JBM "TSR" Compound 77mm diameter  Part M-77
The first step to install the new diaphragms is to cut both the
plastic retaining washers from the original slides as shown.
( Remove stuck slides by placing carburetor body under a
100 watt lamp to warm it and soften varnish. )
Tire is slightly undersize to hold diaphragm on slide.
Install the new diaphragm by pushing it over the lip on
the old throttle slide as shown. Hard rubber tire fits tightly
to slide. We are asked about adhesive on this part, and  
"Super Glue" will work. Do not use other adhesives.
Remove sharp edges that can cut the diaphragm.
Use fine sandpaper or Scotch-bright pad to clean
the mechanical lock groove and remove any
sharp corners that might cut the diaphragm.
Use Crazy Glue or Super Glue on a clean slide. Prevents rotation.
Install your needle and clip as shown here.
Slide cut-away MUST face proper direction.
Position the throttle slide and diaphragm as shown with
the cut-away facing the open mouth of the carburetor.
Roll the diaphragm a bit to push it into the groove.
Place a dot of paint at the "key" tab location for easy
future removal and positioning.
Place the slide return spring and check that the
diaphragm rolls properly.
  • Install the top cover and check for smooth
  • A smoothly moving slide is needed as only a
    very light return spring returns the slide.
  • A small hole in the throttle slide is what allows
    the venturi vacuum to operate the slide. This
    constant velocity carburetor prevents stalling
    and gives smoother running than other direct
    acting carburetors.
  • Some folks want to use Super Glue adhesive
    on the slide, and this will not harm anything, but
    be sure not to get adhesive on the sides of the
    slide. (This prevents rotation or removal.)
Note: Never use carb cleaner or compressed air.

  • BS38 carbs use 77mm diaphragms
  • BS34 carbs use 73mm diaphragms
  • BS34SS carbs use 70 mm diaphragms
Only $19.50 each
To order:
Go to

email: sales@jbmindustries.com
Domestic Shipping only $8.00 per
order for any number of diaphragms
Be sure to visit our page
for Carburetor holder
socket boots for Yamaha
650 twins.
See Carb Holder Button
ORDER: MIKUNI BS38-CV Diaphragms if you
have a Yamaha 650 twin made from 1970 thru
end of 1979, or early XS1100  M-77
Later used 73mm diameter BS34.
Measure !
ORDER MIKUNI BS34-CV Diaphragms if you
have a Yamaha 650 twin made in 1980 until
end of production. M-73
Step #2
Step #3
Step #4
Step #5
A finished Mikuni BS38 CV carburetor
Step #6
Step #7
Last updated 09/16/18
This is a photo of a pair of diaphragms or
bellows that you will need to restore your
BS38CV fits these models that we know of:
Yamaha XS-650 1970-thru 79
XS 650 A,B,C,D,E,F,SE,SF
TX-650 XS-1, XS-2, XS500
XS1100  EARLY  &   BS34 Fit  later models.
Note: There are 2 types of BS36CV carbs, and
could be fitted with 77 or 73mm diameter.
Mikuni BS34 is one of the most popular types on bikes of the 1980's
Use your thumb to lift slide open
Air Hole Location should be kept like original.
Special note when installing BS34CV & BS34SS  
Diaphragms and slides:
While your BS34 slide may not have a cut-away as shown
on the BS38 above, it is important that the vacuum hole is
positioned towards the engine side.
The "Hard Rubber Tire" is what
holds the diaphragm to the slide.
MEASURE diameter before
you order
as not all BS34CV
carburetors use the same
diaphragm !!  Most common
mistake  when ordering
BS38CV                77 mm OD of Diaphragm
BS36CV      73 or 77 mm OD of Diaphragm
BS34CV                73 mm OD of Diaphragm
BS34SS  & BS32  70 mm OD of Diaphragm
Mikuni SIZES we have at this time:
Note: BS36 CV carbs were used on certain
FJ1200, 86-93
XJR 1200-1300
XJ900 F
measure OD of Diaphragm to be sure.  
SEE NOTE: 73mm fits Yamaha Venture
To see if you need new
diaphragms, just hold your old
diaphragms up to a strong light. If
you see any light passing
you need replacements.
Air holes must be in proper position for diaphragm to work properly.
BS34SS CV Carburetor Diaphragm is shown above and below.
The outer diameter of this diaphragm is 70 mm   
Part M-70
Mikuni BS34SS Carburetor Shown here takes 70mm diaphragm
BS34SS CV Carb
has a 70 mm diaphragm
Click here to go to
Keihin Carburetor
Diaphragm page.
Click here to go to
Keihin Carburetor
Diaphragm page.
Click here for more info
Yamaha 650 information.
Need more info? Click here.
Need more info?  CLICK HERE !
Click here to see
  • JBM Diaphragms are very heat resistant and can run in fuels
    containing ethanol.
  • JBM Diaphragms have a "rolling" action and resist twisting of
  • JBM Diaphragms are easy to install and eliminate leakage at
    plastic rings. Less expensive than other types of replacements.
Click here for HOW TO MEASURE
Yamaha Venture Notes:  The 73 mm Mikuni Diaphragm fits the Venture models even with plastic slides.
Remove the short metal tube from the plastic slide if loose, and remove the rings. Place the JBM Industries
diaphragm on the metal tube, and then push tube into the plastic slide. Use Super Glue on metal tube. If metal
insert tube is not loose, just cut the rings off plastic slide with side cutters as shown.
SEE NOTES on Yamaha Venture installation shown down page.
CLICK HERE for our "How to Order" Page.
CLICK HERE for our "How to Order" Page.
CLICK HERE for our "How to Order" Page.
How to measure page.
Click here to see how to remove and restore a damaged slide.
Like to know about JBM Industries? Click here.
Click Here for the "How to measure" page and a
listing of rough dimensions of our manufactured
M-73 Diaphragm
M-73 Diaphragm
Click here for "How to measure"
and dimensions page with Q & A.
NOTE: Order M-H-68-S for Mikuni 28mm diaphragms for 1980 XJ650
Have a question about diaphragms?  CLICK HERE
Just to say thanks! The diaphragms arrived on Friday
here! That's quicker than parts I ordered from the UK
and still haven't arrived!
Very pleased with the quality too. The bike runs great
with them...Thanks again, Paul,  England  M-73
Hello Don,
So the 4x diaphragms arrived last Thursday the 4th.
My Bike is a Yam FJ 1200 “3CX”  with Mikuni BS36 .
The job to do is to cut and disassemble the 2 plastic
rings on each sliders then your part “Mikuni M-73 “ fits
Then taking care about the orientation of the sliders
before closing.
My bike runs well now , Thanks a lot!
David Batellier
Gidday Don
I have already restored a 1980 XS650SG and a 1981
XV1000RH, and fitted your replacement Vacuum Slide
diaphragms to both Makuni and Hitachi carbs.
They work great with total reliability.
I am now restoring a 1979 Yamaha XS750F which is an
Australian production bike.
The bike is all original and fitted with Mikuni BS34-11
I would like to purchase 3 replacement diaphragms to
suit the BS34 CV carbs.
The fitment of the Mikuni 70 mm diaphragm of the BS 34
SS CV works on the Mikuni BS 32 that is on my 1982
Kawasaki 650 H2 CSR also.  Awesome fit and one of the
easiest replacement parts I have ever dealt with.  Just as
you said it would on your website.
JBM also makes a 68 mm
Diaphragm that fits many smaller
Mikuni & Hitachi carburetors.
Please measure  M-H-68-S
If you think you have BS34SS
carburetors: be sure to measure to
groove OD.  Do not trust manuals, spec
sheets, or other owners.  MEASURE !
We got your diaphragms for a buddy’s Yamaha 500 last year and they put the OEMs to shame. I had them on the
slides in 10 minutes. Thanks for a great product!
From: J. Jay Wilkinson BREJAY@Centurytel.net
Went to your website on Friday, 13 December, and just
finished installing your 73 mm Diaphragm on my Mikuni
BS34. The installation was a breeze and I couldn't be
more impressed! What an excellent product, and I
believe you have done a real service for those of us
with old bikes. I'm sure this will make my Yamaha SR250
"Café Racer" happy. Thanks again, and,
The 70 MM diaphragm I ordered
works great in my Mikuni Carb,
although it wasn’t designed for this
(2000 Arctic Cat 4X4 ATV 300cc)
Your product is far less expensive
than OEM at $139.  Please let me
know if you decide not to carry or
produce the 70mm diaphragm as I
will need to order a few spares.  
Thanks again for a great product and
fast shipping.    ....Ben Stacy
I am very pleased your fast delivery.
diaphagms were very easy to fit mine cv36 Mikunis.
And i tested them and finally my bike goes to
rich, another time without new diags it goes
lean and causing engine to overheat.
my bike is fj 1200 yamaha.

By the way ordered diags 01.08.2014 and got
them to my home 08.08.2014 to Finnland, so
Mikuni BS28 & 30 diaphragm 63mm OD for XJ550R,FZ600,YX600
Click: HERE
After you measure:

Click here for HOW TO ORDER.
Thanks Guys:
My lil get around town cruiser was dead in the water. The dealer parts are
to expensive and I was gonna part her out. Your diaphragm
M73 fixed my
issue and was a breeze to install.  Although, I admit I read as much as I
could on your website  first.
Thanks A Million, Mark Billings, Happy as hell in Sacramento