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Old 11-09-2014, 02:03 PM   #1
victorlaszlo OP
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Bing carb - diaphragm ok?

Am about to rebuild my carbs, took them off today and had a look at the diaphragms.... Although they are fresh, good soft, rubber and no cracks they seem to be "too big" - can that really be? Could the previous owner have fitted the wrong ones? Or do they expand with time...?

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Old 11-09-2014, 02:18 PM   #2
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Do they fit when the slide is pushed upward some and the diaphragm is "domed" slightly? If so, then they're fine. They won't fit when they're flat, at least not without some ripples in the material. And yes, they do seem worse when they are older.
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Old 11-09-2014, 03:44 PM   #3
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I don't know if it's the petrol these days or poor quality diaphragms, but the ones
on my 79 are the same, I took a top off one and the diaphragm would not go back
in, I've made a mental note to buy them from bing in the future
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Old 11-09-2014, 03:47 PM   #4
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Do they mix alcohol (ethanol) into the fuel over there?

Also are they wet with fuel/oil up top? If so, that's not normal. They should be dry.
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Old 11-09-2014, 03:51 PM   #5
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Alcohol in the fuel isn't the trouble. It's people squirting Gunk carb cleaner or the like into their carbs. Don't do that! The crap swells rubber and ruins it. That's the downfall of many a diaphragm and O-ring. Gas is no trouble.
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Old 11-09-2014, 04:00 PM   #6
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Over here fuel is very much a problem, smuggling over the border and other
associated activity means it's very hard to get some that hasn't been messed
with, lately the scumbags are 'lengthening' petrol by adding kerosene

Doubt it's like that for victor in England, though you never know. I only have one
set like that so I had kinda thought it was the quality of aftermarket diaphragms
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Old 11-09-2014, 04:05 PM   #7
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Quote:
Originally Posted by rambozo View Post
Over here fuel is very much a problem, smuggling over the border and other
associated activity means it's very hard to get some that hasn't been messed
with, lately the scumbags are 'lengthening' petrol by adding kerosene

Doubt it's like that for victor in England, though you never know. I only have one
set like that so I had kinda thought it was the quality of aftermarket diaphragms
The aftermarket diaphragms that I have seen sold at Motobins/Capital Cycle type places are junk but that goes for most of the aftermarket crap places like that sell. The crap has become so popular that now BMWNA is selling it as genuine BMW parts in some rare cases.
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Old 11-09-2014, 04:30 PM   #8
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i go to motorworks, it's most likely they sell the same ones as motobins though.
It's super annoying fitting them on flat top bings so I'll definitely be going genuine
from now on
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Old 11-09-2014, 05:14 PM   #9
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Quote:
Originally Posted by supershaft View Post
Alcohol in the fuel isn't the trouble. It's people squirting Gunk carb cleaner or the like into their carbs. Don't do that! The crap swells rubber and ruins it. That's the downfall of many a diaphragm and O-ring. Gas is no trouble.
I once cleaned a wheel in my younger days with Gunk brand engine degreaser. It ran off into the bead area of the tire.. I went indoors for the night. The next morning I came out and the bottom of my motorcycle tire was the size of a basketball and about to burst like a bubble. The engine degreaser had completely disolved the rubber overnight.
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Old 11-10-2014, 01:30 AM   #10
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Quote:
Originally Posted by silverhead View Post
I once cleaned a wheel in my younger days with Gunk brand engine degreaser. It ran off into the bead area of the tire.. I went indoors for the night. The next morning I came out and the bottom of my motorcycle tire was the size of a basketball and about to burst like a bubble. The engine degreaser had completely disolved the rubber overnight.
Yeah alcohol is no problem, much less aggressive on most plastics and rubbers than petroleum (hell, we can even drink it without damage). Here in the UK though it's a popular urban myth that ethanol ruins your engine in the most remarkable ways (although from my POV it's most often just used to blame poor maintenance / faulty setups).
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Old 11-10-2014, 01:34 AM   #11
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Quote:
Originally Posted by silverhead View Post
Do they mix alcohol (ethanol) into the fuel over there?

Also are they wet with fuel/oil up top? If so, that's not normal. They should be dry.
They felt a bit oily, but i wouldn't say wet. Also I placed the carbs up-side-down before opening them up which might have caused that...

So, the diaphragms should only fit with the slide pushed upwards.

If they still don't fit and new ones are needed, are you saying that the motorworks versions are rubbish and I better get them straight from Bing?

Does Bing have a British outlet?

Regarding the rest of the o-rings etc - I suppose I can get that from motorworks right?

Many thanks Vic
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Old 11-10-2014, 01:52 AM   #12
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Quote:
Originally Posted by supershaft View Post
Alcohol in the fuel isn't the trouble. It's people squirting Gunk carb cleaner or the like into their carbs. Don't do that! The crap swells rubber and ruins it. That's the downfall of many a diaphragm and O-ring. Gas is no trouble.
Man, it's the rubber. It's the same as used in your shorts. That stuff just don't last.

Stuff them back in properly, or buy a new set from whoever, put 'em in and don't touch for 5 years. YMMV
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Old 11-10-2014, 02:36 AM   #13
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I would say motorworks would do genuine ones if asked, I have spares so I didn't
order a new one to find out. I have fitted their o rings with no problems on 3 bikes.

me109s advice of not opening them for five years is what I'll be doin from now on,
most likely when you have the new top on you won't need to
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Old 11-10-2014, 05:10 AM   #14
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Motobins do both genuine and pattern diaphragms and there is a huge price difference. Genuine are 22.00 each and pattern are 8.40.

The pattern ones are claimed to be genuine Rover and approved Saab spares which means they are Stromberg carb spares. I believe there is a difference in thickness and therefore response may suffer and that might be a reason not to use them but last I heard Rovers and a Saabs used the same fuel we do.
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Old 11-10-2014, 06:30 AM   #15
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Great - thanks for all replies guys!

Will investigate if they can be fitted using the method outlined above tonight. Otherwise I'll go for the genuine ones, 22 isn't that bad after all, was expecting 50 LOL
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