|To order: We need the make of carburetor and outside groove diameter.
Measure the carburetor groove, NOT the old rubber.
Example: Keihin 71mm State how many you need. ($19.50 each)
Please tell us what country you are in. We ship after you pay.
We will send you a Pay Pal Invoice for you to pay if you approve.
|JBM INDUSTRIES manufactures diaphragms to fit constant velocity "CV"
carburetors used on certain older vintage motorcycles.
JBM is a part manufacturer and makes only the parts. We cannot give advise on
carburetors, jets, or engine problems.
JBM does not know which diaphragms can be used on your vintage motorcycle or
how many carburetors it has. The buyer must measure his carburetor body as
shown. Be sure you know carburetor maker. Years and countries vary.
Never try to measure the old rubber as it may be swollen or have shrunk out of
the original dimensions. Measure the carb body only!
The best way to get the correct size is to measure your carburetor as changes were
made for different years and in different countries. The listing above has notes on
what buyer's have reported they fit. These diaphragm dimensions may fit many
other models not listed.
The JBM diaphragms all work on the same principle; in that a thick rubber tire that
has a minimum amount of stretch is used to replace the plastic or metal rings
that originally clamped the diaphragm. These rings are removed with small side
cutters after clipping in several places. The JBM diaphragm is held in place by
tension of the tire in the groove on the slide. The hole in the tire is usually a
millimeter or two smaller than the groove diameter on slide, and this creates the
Do not over-stretch the tire! Do not bend the tire!
Some diaphragms might need to be held with adhesive such as Super Glue .
Super Glue for clean metal slides. Use only a minimum amount as solvents can
attack the rubber. Keep any adhesive off of the sides of the carburetor slide.
Never spray compressed air or carb cleaner in jets or holes while diaphragm is
installed in the body.
This method of diaphragm replacement relies on the installer to get the slide back
in place with the original alignment, and no "key" is used. Once correctly positioned,
a dot of paint aligned with the "key" slot can make removal and replacement of the
slides fool proof if you need to change the needle.
|JBM "users tell us" diaphragm size chart for CV carburetors we manufacture diaphragms for.
|This list means only that these diaphragms fit "some models" of the motorcycles shown. Different years and countries change usage. YOU MUST KNOW WHAT CARB
YOUR BIKE IS FITTED WITH. --- JBM Industries cannot provide you with any information as to what fits your bike, other than shown on these pages.
The same model motorcycle might be listed in several places due to different carburetors in different countries. JBM sells to motorcycle repair
professionals only. You must be sure to install the diaphragm by rolling it when you put the cover on the assembly. Some "Hacks" by owners are listed.
|Remember that to be SURE of the
correct part you MUST measure goove
diameter. Know carburetor brand !
Shop and owners manuals can be
wrong! Different carbs may be fitted in
different countries on different years &
models. MEASURE !!!
|Questions and answers about JBM Industries replacement diaphragms for vintage motorcycle CV carburetors.
|Q: What type of adhesive do I use to keep the rubber on the slide? I am afraid the slide might rotate. ( Cyanoacrylate )
A: Use regular Super Glue sometimes called "Krazy Glue" sold at Dollars Stores, Auto Parts Stores, and Discount Stores to glue rubber to metal slides. To glue
to plastic slides, use Super Glue. Use only a small drop as it can run off very quickly as it is thin like water. Take great care not to get any on the side of the slide,
as it must move freely. Dry fit first to be sure everything is correct before you glue, as positioning time is limited to 0 sec.... Use glue sparingly, as solvents are
not good for the rubber. Never use Silicone sealant. -- Do not try to "repair" holes in the diaphragm. Never spray carburetor cleaner around the outside or in
passages while diaphragms are in the carburetor. Never use fuel system cleaner or octane booster. These solvents will swell the rubber and contaminate it.
Q: What does the dimension "Dish" mean?
A: It represents about 1/2 of the travel that you can get with that diaphragm. Slides usually do not close the carburetor bore completely. The slides move from
about 1/4 throttle on up. "MODEL" means the original carburetor the part was designed to fit, but it might fit many other types as well. Outer groove depth,
width, and design can be different, so you need to watch those dimensions. The hole in the middle should be about 2mm smaller than the root diameter of the
groove in the slide with plastic ring removed, so that there is some tension on the tire. As an example, the 68mm Hitachi diaphragm seems to fit a Keihin
carburetor used on a Honda. These part dimensions are given above so you might be able to fit one of our diaphragms to other carburetors.
Q: What can I do wrong installing these?
A: Failure to position "air hole" in the slide correctly when you place it back into the carb body. ( Do them one carb at a time. ) Failure to remove sharp or rusty
edges that could cut the rubber. Over-stretching the "tire", as the rubber is designed to not have much stretch and contains no fabric. Be sure slide groove is
clean and free from oil or grease. Failure to "roll" the diaphragm material when installing. .... If you find these instruction confusing, please don't try it.
* If you are using Super Glue ( Cyanoacrylate ), don't get glue on the sides of the slide, and use only a very small amount. ( Super Glue and Krazy Glue are trade
Most enthusiasts have no trouble. Look at all the photographic instructions for all carburetor models to get an idea of how they work. While JBM diaphragms
are easy to install, some enthusiasts are very poor mechanics and should know their limitations. Take the carburetor to an expert. * MEK, Tolulene, Acetone,
Carb Cleaner, fuel stabilizer, paint thinners, etc. are solvents that destroy rubber or cause it to swell or shrink. There is not much force to cause slide rotation, and
the thin rubber diaphragm will not be able to resist any twisting force anyway. There is no mechanical key on the slides. Follow instruction carefully and do not skip
any steps. Do not substitute with your "favorite" adhesive. Always "Dry fit first" to be sure you have everything correct.
Q: How long will these last? How will they affect my performance?
A: We really don't know an "exact" answer to this question as we have only been making these types for vintage motorcycles for about 5 years. We have been
making diaphragms for other uses since 1978 that work in a similar manner. TSR material is superior to the original. We think it fair to say you should get at least
5 years out of them, but a lot depends on installation. We have sold more than 4000 of these diaphragms. They will probably outlast your originals. Note: An
engine that backfires due to lean mixture, bad plugs, valves, etc. can break or destroy the diaphragms. Never blow with an air hose in passages with
diaphragms installed...These diaphragms should make your engine run like new, but will not cure all carburetor and fuel delivery problems. Manifold vacuum
operates the slide and is very powerful, just like power brakes on a car. Diaphragms have nothing to do with your idle. We have many testimonials at the bottom of
installation instruction pages. Please check them out. CLICK FOR INFO...!
Q: I don't see my bike listed. Do you have a diaphragm that fits? I see different diameter diaphragms listed for the exact same bike. How can this be?
A: The chart at the top of this page serves only to inform that we might have what you need, or that someone has used some JBM diaphragms on a bike and it
worked. In most cases you should measure to be sure, and look to see what make of carburetor is fitted to your bike. Some carburetor changes were made mid-
year and some foreign bike might have different carburetor models. If you don't see your machine listed above, there is a small possibility that one of the above
diaphragms will fit, but you better do a lot of measuring before you order. JBM does not make all sizes for all bikes, and we try to manufacture for vintage or
collectible motorcycles as much as possible. You can return undamaged diaphragms that don't fit, but JBM does not refund shipping and handling costs......SO
check model & measure to be sure.
Q: My slide has a metal top ring. I need to slide the diaphragm up the slide as it is the only way I can get it on. Is this OK?
A: No. You MUST cut off the metal ring. Sliding it up the length of the slide will ruin the diaphragm. JBM diaphragms are made from a rubber that has very
limited stretch. JBM diaphragms MUST be installed from the top. Please look at all pages of instructions on this site. Metal rings must be removed from the
slide by cutting in several places with side cutters. ( Twist the cutters back and forth. ) If you are unable, or unwilling, to install by removing the rings, please
return the diaphragms for a refund. Only plastic slides have a molded lower ring that cannot be removed, but the JBM diaphragm is designed to fit these, and a
small amount of Super Glue Gel type adhesive must be used to install them on plastic slides.
Q: You list a diaphragm that fits a Mikuni BS34 carburetor. I have a BS36 carburetor and wonder if it will work?
A: Yes. It will work. Many carburetors use the same housing and slide, but the bore in the throat is different. JBM stamps the diaphragm for the carburetor
model number that it was originally designed for, - but it might fit several different models of carburetor. Measure the groove OD, as that is the best way to
judge a carburetor series, as the slides are usually the same. In some cases a diaphragm from a different brand of carburetor will fit another brand. Measure
the outside diameter of the groove! Be double sure to measure correctly if you think you need Mikuni BS34SS ( M-70 ),-- as early or foreign bikes might not be
equipped with these no matter what your manual says.
Q: I have a bike model that is not listed and live in a foreign country. Can you tell me what diaphragm to order and do you sell needle jets?
A: No. JBM Industries cannot tell you what model carburetor your bike has. We have no motorcycle parts, and are not motorcycle enthusiasts. We know nothing
about your bike, and only you can decide what diaphragm to order. We do NOT have all sizes for all bikes. We will ship to most foreign countries with no problem.
Q: I just bought my used bike and need to clean the carburetors. How do I get the slides out?
A: Remove the screws that holds the cover, and the rubber diaphragm should lift out. If your carburetor is full of varnish from evaporated fuel, the slide might
be very stuck. You must remove the carburetor, and place it under a lamp to heat the body. When hot, the slide should pull right out, unless someone has
butchered it by using force.
NEVER use compressed air to blow through jet holes unless you remove the float bowl first, as air pressure will collapse and crush metal floats. Do not soak or
spray carburetor cleaner on rubber parts. .... Slide removal and broken slide repair can be seen if you CLICK HERE.
Q: My old slide diaphragm had holes in it, and I tried to fix it with glue. My diaphragm seems too big to fit in the groove now. Do I need a new diaphragm?
A: Yes. Your old rubber can be swollen by the solvents in the glue or ethanol in the fuel. Carburetor cleaner can also cause rubber to swell. The rubber swells
because it absorbs the contaminant, and this will also soften and weaken the rubber so it tears more easily. -- You can also have rubber get harder from
getting the plasticizers ( Softening oils ) washed or leached out of the rubber. All rubbers get softer and expand when heated, and most motorcycles have
carburetors mounted where they will get hot. Heat can cause rubber to rapidly age. JBM uses very high quality and temperature resistant rubber stock that
works well with 10% ethanol auto fuel.
Q: Will new diaphragms improve the performance of my motorcycle?
A: That depends on how bad your old diaphragms are. Diaphragms control performance at speeds above 1/4 throttle. They don't affect your idle mixture. Some
things to check before you order new diaphragms are:
Q: I recently ordered a set of carb diaphragms for my '74 Honda CB360 and when I got them they fit perfectly and performed well as stated.
However, I just had a mechanic service my carbs in pursuit of another problem, and they apparently blew carb cleaner through the jets and passages with the
diaphragm still in place. When I got them back I took them apart to see what happened, and found that the diaphragm has (not surprisingly) increased in
I know this is not the fault of your product, but rather my idiot mechanic -- but was just wondering if perhaps the rubber will shrink back to it's former size after
drying out, or if these are ruined and I need to order new ones?
A: Carburetor cleaner will contaminate any rubber and cause it to swell. You can try baking in an electric oven at 250 degrees F for an hour or until the rubber
shrinks. If that does not work, you will need to buy new ones. Never blow out passages with compressed air or carb cleaner, as it can collapse floats and break
or swell diaphragms. Diaphragms normally are dry and never get liquid fuel on them.
Q: I recently ordered diaphragms, but did not measure the outer groove as it was listed as fitting my bike on your site. My bike has a different brand of
carburetor and these parts will not fit. What do I do?
A: Return the unused diaphragms with a note stating what size you need and S/H in cash or stamps for shipping & handling, and we will exchange them for you.
Should you wish a refund: Please be sure to include your INVOICE NUMBER that you paid from Pay Pal.
NOTE: Only unused and undamaged diaphragms can be returned. If you glue it or modify it, it cannot be returned. Must be in saleable condition.
|JBM Diaphragms do not have a "KEY" in most cases. The installer MUST position the slide when fitted. A mark of paint can serve to align the
diaphragm and slide assembly for future use. NOTE: These diaphragms require some mechanical ability and knowledge to install.
For balance: Be sure to replace all diaphragms at the same time. ( If you have mechanical ability, you would know that. )
|NOTE: The listings below are meant as a guide. You should still MEASURE. This information only means that it worked for "someone", & you might not have stock carburetors.
Our thanks to those that have sent us this information. FIRST STEP: IS TO BE SURE WHAT BRAND OF CARBURETOR IS FITTED TO YOUR BIKE...!!!
NEXT: ARE YOUR SLIDES MADE OF PLASTIC? Plastic slides require sharp cutters & much careful handling to install. Not for amateurs !
|Note: Please be sure you have spent at least 30 min reading
the information on this web site before you order. Be sure to
click on links to see instructions and special notes about
your installation. See Q & A below.
|Shipping and handling for ANY number of diaphragms is only $8.00 for domestic. -- $35 Foreign & $28 Canada These items are very light & sent by mail.
| Here’s a way to get the diaphragm rings off without leaving the slide with hack marks: Simply use a Dremel with a small wire wheel at SLOW speed and go wire out the
rings till your almost to the slide. The wire wheel eats the plastic without damaging the aluminum, sorta like when the doc removes a cast without cutting your skin. Then you simply use
the pliers to snap the rings off.