Symptoms of small hole in carb diaphragm

[rockford]

On a 4 cylinder GS, if one diaphragm had a small hole in it, how would you ever know? If you want to guess, that's OK but if you know the answer, that would be much better. (By the way, I don't have that problem but have seen damaged diaphragms discussed here lots of times without any mention of symptoms.) Thanks for your thoughts!

[Steve]

I have not experienced the symptoms myself, but reduced performance would be one symptom.

The function of the diaphragm is to lift the slide. The slide is basically a variable venturi. If it is not lifted by the diaphragm, it becomes a restriction, not allowing full air flow for proper running. That will definintely reduce overall performance.

If your holes are still on the small side, the slide might be lifted, but a bit slower, and maybe not lifted quite as far, due to the leak. Still results in reduced performance.

Many "fixes" have been proposed, but most of them fail due to the gasoline vapors and/or flexing. The best solution is replacement. OEM replacements are prohibitively expensive, one reasonable alternative is JBM Industries.

.

[rockford]

Yes, I'm sure performance would suffer or else nobody would ever know they had a problem. My own guess is that it would be most noticed at idle and diminish as RPMs are increased.....but I'm hoping someone who's experienced it will tell us about the particulars. As far as replacement, they're on Ebay all the time but the prices are usually ridiculous. I've got extras so I'm sure I'll never be shopping for one.

[60ratrod]

I used them last year for the carbs on my kz. those diaphragms work great. clipping the plastic rings can be a pain though.

[JTGS850GL]

I have some spare diaphragms with slides available for a BS34SS. Let me know if you're interested.

[Gorminrider]

It's a good question because telling a complainant to adjust their idle mix or synch the carbs etc. would go no where except backwards. A good "cleaning" might find it but only if the complainant is specifically directed to check the operation after reassembly-by plugging the port and seeing if the slide stays up..something that is not in the manual to my recollection.
Perhaps it's easy to generate symptoms without removing the airbox...loosen the top of one carb . Or if the trouble is taken to block the vaccuum port. A symptom of not raising the needle would make one lazy cylinder, and very difficult or impossible to synch... but the size of the hole or tear might be important. a tiny tear might self-seal to some extent on changing vacuums and only exhibit symptoms on a steady throttle as the slide drops....

[Steve]

... Or if the trouble is taken to block the vaccuum port. ...

What vacuum port needs to be blocked?

.

[hillsy]

My own guess is that it would be most noticed at idle and diminish as RPMs are increased.....but I'm hoping someone who's experienced it will tell us about the particulars.

You wont notice anything at idle. If you take your airbox off and start the bike / let it idle you will not see the slides move at all. It is only when the bike is revved that the slide starts to move.

Usual symptoms of holes in the diaphragms are a sluggish throttle response. But, if there's just one tiny hole in one diaphragm out of the four then you may not notice it at all.

[rockford]

You wont notice anything at idle. If you take your airbox off and start the bike / let it idle you will not see the slides move at all. It is only when the bike is revved that the slide starts to move.

Usual symptoms of holes in the diaphragms are a sluggish throttle response. But, if there's just one tiny hole in one diaphragm out of the four then you may not notice it at all.

Based on a bunch of research, I think you've got it just right. In addition, you would get very poor gas mileage.