new diaphragms!

[mr blackstock]

G'day,

I recently bought 4 replacement diaphragms from:

http://jbmindustries.com/

for my FJ1100 1985 and installed them just the other day, what a difference!  Instantly she idled sweet, pulled stronger than before and had less vibration.  The old diaphragms were not bad, just lots of pin pricks.

The diaphragms were cheap, only $20 each, easy to install and were a very tight fit on the slide.  I have been using diaphragms from this company in my XJ650 for around a year now with great results.

Cheaper than genuine Yamaha stock too.

cheers, Gareth

[yamaha fj rider]

Thanks for the report on the JBM diaphragms. Good to here it worked out, and much cheaper than Yamaha.

Kurt

[bigbore2]

Yep, that is a golden find.  I remember reading about them a year ago and someone was going to test them out and report back, but I will take your word for it that they work well. 

[RichBaker]

Which ones did you get? I see several listed, but not the FJs.

[aviationfred]

Which ones did you get? I see several listed, but not the FJs.

I found this on the JBM site.


Mikuni                 BS34CV & 36         73mm dia.                     25mm dia                       4mm                         19mm         Fits Yamaha 650 twins '80 on, FJ1200, BS36, XJR1200-1300
M-73                                                                                                                                                                             XS250, SR250, XS400, Venture, XJ900F, XS750 & XS850 triples
                                                                                                                                                                      Virago XV535, XV500 XS1100, & Mikuni BDS34-Downdraft carburetor.
                                                                                                                                                                      Kawasaki GPZ750 '82-'83, KZ1100,
                                                                                                                                                                      Suzuki GS450E, GSX1100, GS1150, VZ400 Desperado/Marauder

Fred

[RichBaker]

Thanks, I was looking around, but missed that...   

[racerrad8]

...I remember reading about them a year ago and someone was going to test them out and report back, but I will take your word for it that they work well. 

There was a report posted last year and is linked in the carb section in the files; Replacement BS36 carb diaphragms

When you scroll down there is even a pictorial from Dads FJ when he replaced his a little later last year.

So, you have more than one persons word they worked well.

Randy - RPM

[mr blackstock]

If you do intend on ordering a set, be sure to measure your carbs for a exact fit.  I imagine many of the FJ's used the same carbs, but it is always best to be sure.

Also, I just read the above link posted by Randy, (sorry for not watching the forum) and it may be worth noting that they are slightly thicker.  When I installed them in my XJ650 I was worried about the difference in the way the slide is lifted under suction with the slightly thicker diaphragm.  After installation I honestly could not tell any difference, so I threw a pair in the FJ, still no difference from the old ones.

Bear in mind though, the stock diaphragm's end up having "folds" from the way they are lifted from the suction, over time I imagine this would cause stiffness in the way the diaphragm lifts the slide.  The JBM diaphragm's, while not as light as the stock, do not fold.

I would be good is someone could bench test both types using a air flow test and a resistence meter on the different diaphragms.

cheers, Gareth

[andyb]

Bear in mind though, the stock diaphragm's end up having "folds" from the way they are lifted from the suction, over time I imagine this would cause stiffness in the way the diaphragm lifts the slide.  The JBM diaphragm's, while not as light as the stock, do not fold.

Can you describe this a little better?  I think I know what you mean, but I've never seen it in a reasonably healthy carb before.  I've seen old slides that I left on the bench appear to have their diaphrams dry up and take a set in a crinkly position, but not on anything that's not just sitting. 

[pdxfj]

I think what he's trying to describe is the stock diaphragms create a fold around the edge where the cap holds them into place.  It's around this fold where pin holes and tears can occur.

Think of folding a piece of paper in half..over and over and over and over and over again on the same fold line. After a while you'll wear though the paper.

Dunno if that makes any sense.. ?!?!?

[mr blackstock]

Hello,

"pdxfj" is describing well the issue of the diaphragms getting folds, and excessive wear occurring in these folds.  The wear is not entirely where the cap holds them in place, but on the body of the diaphragm. 

It is worth noting that it took 25 years of "up and down" for my diaphragms to get bad enough for me to replace them, so I am not saying the originals are faulty or poorly designed, quite the opposite in fact, it is for this reason they are expensive to replace because Yamaha use very good materials.

I mainly mentioned diaphragm folds to illustrate that while the JBM diaphragms are slightly heavier compared to original diaphragms, considering how folds may create the same "resistance" to movement as heavier material, it is my opinion the difference is slight, if any.  IMHO.

I realise people are worried about using unorthodox methods to maintain their machinery, but this product was also used in a local motorcycle magazine article specifically to replace existing diaphragms.

cheers, Gareth