Aftermarket CV carb diaphragm replacements - anyone tried?

Hi,
Since I have holes in all my Mikuni BS34 and BS36 carb diaphragms I thought it might be best to take a look for the alternatives and ran into this website.

JBM industries diaphragm replacements

Looks good to me but I figured I'd ask the question whether any of the XJ'rs
here have any experience with these replacements?

 

I havn't tried them myself, but it looks like you struck gold...

 

I have never personally tried them but i herd of a lot of virago owners using them

 

After reading about the process and all the other bits on the site I'm thinking they are going to work a charm too.
Just ordered them.
I'll do some pics when they arrive, of the procedure.

 

I guess it beats a 25 cent condom lol

 

Funny, ...

Until introduced to this site, ... right now. I have never heard of them!

At $20.00 a-pop, ... how can you go wrong?

I'm going to try them out.

 

Great product!! you will not be disappointed.

 

WOWZAS!!! Now where are the 28mm Mikuni parts?

 

Did you replaced all 4 - or just what was needed??

Reason for asking is that I only need 1

Thank You

Stephen

 

They're not for the Hitachis.

Or smaller Mikunis.

Yet.

 

For HSC32's

JBM - Hitachi

 

As the operator of JBM Industries, I have been asked to reply about the diapragms we are making. We have been manufacturing the diaphragms for Mikuni BS38 carburetors for over a year now. These were used on Yamaha 650, Kawasaki KZ750, and many other motorcycles.
We are now making diaphragms for some Hitachi carburetors used on Virago, Seca, and Maxim models.
My problem is that I make parts, but don't know very much about the motorcycles that they fit. Folks wanting diaphragms should measure the goove diameter with a caliper to see how many millimeters the diameter is.
Right now JBM makes 9 sizes for older motorcycles. Mikuni, Keihin, and Hitachi. People with questions should visit the JBM web site. www.jbmindustries.com. We do recommend you replace all diaphragms at once, rather that just one. We use real high quality rubber that should run your bike another 30 years. I don't plan on making more tooling this summer as things are getting too complicated. You may also find JBM parts on Ebay at times, but they cost a bit more because of Ebay fees.

 

The XJ550s used Mikuni BS28s. I'll measure one later today and post; it would be great if you have one available that fits that carb too.

The Hitachi availability will be good news to a large number of folks on this forum, myself included (I also have a 650 with Hitachis.)

Keep up the good work. This is a long-needed solution.

 

I think we make the diaphragm to fit the Hitachi used on the XJ550. Look and see if it measures 68mm on the OD.

 

The XJ550s didn't use Hitachis. Mikuni BS28.

 

If your bike has Mikuni, it would be a 73mm diameter or a 70 mm I think. Those are the only two we made for around that year.
You see my problem. I have parts but don't know what fits. I don't even know how many cylinders it has.

 

Welcome to the site JBM !!

 

I could possibly trade you a full rack of XJ750 4x carbs (dirty) for full set of 4x diaphragms that fit :wink: (Then you'd have a size sample and a set for assembly pictures).

(I forget what brand/size they are)

 

Re: Aftermarket CV carb diaphragm replacements - anyone trie

All I really need would be one carb body and slide. I really think the Maxim has Hitachi carbs, and I have made that mold. 68mm diameter. I usually design the mold, and send back the carb with new diaphragms for the donor that lets me measure it. Pretty sure I got that one. I have a list here that someone in Germany made, ( from experience? ) for different carbs on Yamaha. Carbs might be different in Germany, so I am not sure how much good it does me.

 

The XJ550s, both Maxim and Seca, have Mikuni BS28s. (They're 4-cylinder bikes, like the bigger XJs, but came with Mikuni carbs.)

Most all of the 650/750 series, Maxim and Seca, have Hitachis, not 100% sure of the size, but I think they're 32's.

The 650 Seca Turbo (only) has "pressurized" type Mikunis, because of the turbocharger.

The Seca 900 has larger Mikunis, not sure of the size.

 

Re: Aftermarket CV carb diaphragm replacements - anyone trie

Hi Again,
Just got the JBM diaphragm replacements yesterday and I just had to try them out.
They are damn supple and nice and snug when stretched over the piston, but not too tight as to deform or anything.

Really impressed with the press in fit to the top groove of the carb too. All round impressive and great product, me thinks.

I used the '3' in the '73' on the top of the diaphragm mold as my marker and made sure the diaphragm was on the piston in the right spot by sliding it around while gripping the tyre.

Cutting the lower plastic ring off was a bit tricky, compared to the top one, but I just took my time and worked a groove into the edge before snapping it off.

Mountain of pics below,

 

I got mine re-done at NRP in the UK http://www.nrp-carbs.co.uk/

Did a beautiful job, good service too. Not as cheap as these at 32 GBP each plus P&H.

Cheers Ian

 

Re: Aftermarket CV carb diaphragm replacements - anyone trie

I'm seriously considering these jbmindustries diaphragms as well for my '81 XJ650. Anyone else have any experience with them?

 

Okay, I've got the diaphragms installed (super fast shipping, by the way and Don even sent a replacement when one of the originals was damaged by a staple used to package them). Installation was easy and the bike runs like a champ (or at least without any problems related to the diaphragms).

Now it's just a matter of time to see if they'll last, but I don't have any reason to believe they won't.

 

Fitz, The Maxim-X 700 and 750 have Mikuni BS33 Carbs

 

Re: Aftermarket CV carb diaphragm replacements - anyone trie

Ditto Ditto Ditto!!! Even the pics could have been mine.

They arrived fast, installed easy, very impressed.

 

This dude is making something similar.

Was looking into it when i had an old gpz 600 r with carb issues.

http://www.cameron-site.co.uk/nrp/index.htm

 

I just wanted to follow up and let everyone know I've had these jbmindustries diaphragms for a few months now and not had a spot of trouble so far.

 

alrighty... looks like we are 8 years down the track... which seems insane! but never the less.
I have 2 bikes and this means it is not really that many years worth of on road use.
I have run into the issue that the JBM diaphragms are quite loose on the slides now and the slides are rotating... so far 90 degrees plus on all 4 carbs.
I have fuel on the upper part of the diaphragms also so...
I've moved my floats to the maximum of 6mm and I've decided to anchor the diaphragms in with a layer of RTV. I will post the picture tomorrow and keep you updated on the outcome.
Disappointing hopefully the RTV fix will be the answer!

 

use a fuel resistant rtv

 

I don't know how long JBM has been around, but he's had the XS650 covered for a very long time. The newsletters, forums, e-groups all praise the product. I have never noted a negative remark on JBM.

 

Anchored them with ThreeBond RTV last night. That'll solve it! (I hope)

Yes the diaphragms themselves are great, no doubt, but I have been having this crazy stumble after the bike is hot and I reckon this maybe the cause. I will find out later today of course.

My fix...

 

I think the issue with the diaphragms is more of a flooding issue and ending up with fuel in the chamber above when hot.
Trying to solve by going backwards.

Dropped the fuel level to +1 (6mm).
Putting original needles and lowering by one notch for a test tomorrow. (I had put a kit through and the replacement needles are brass so back to the original aluminium)

The RTV looks great after the test ride today with better (crisp) response but after warming up... back to the serious stumble. (as in pushing off like a bicycle with the bike trying to throw you off once the fuel has cleared)
Fingers crossed... again!

This engine is 1oookm+ after being freshly bored and is not standard (58L pistons in a 31A bore) so... good fun! (grrrr.)

 

RTV was rubbish.
This looks good. At least I have the diaphragms not moving around, not that that was or is the real issue I have. Oh well.

 

Do you think a replacement support ring under the bottom would help keep them stable? I'm looking at possibly ordering a set if available for the bs28.

 

Just to clarify.
The diaphragms are not failing.
They are actually just like new still.

The issue I have is not related to them at all but I did overly state the problem with the slides rotating over time as being the reason I have the problem I have.

The pictures I attached a couple of posts up show a dot (wet spot) where I've glued them with Rapidfix glue to stop them from spinning.

Disregard my previous angst. I should have actually created a new post about the issue I'm trying to resolve.
If I do resolve it I will.

But, I wouldn't hesitate in purchasing the JBM diaphragms. Best thing since sliced bread.