Rob's new brain craves a high "carb" diet.

[Chuey]

On behalf of Rob, I'd like to start a new thread about carburetors and rebuilding them. More specifically, Jean had said something about replacing the diaphragms in her carbs and that it had made a good bit of difference.

My question is, what are the symptoms of needing new diaphragms? Are there visual signs? I have been under the impression that if they aren't torn or don't have holes, that they are OK. Is that a good indicator?

Thanks in advance.

Chuey

[Major Softie]

Yes, there are visual signs. Usually your diaphragms need to be replaced because one or both has developed a hole, tear, or crack. I suppose that they could possibly harden and impact performance, but I've never heard of that happening before.

The most common symptom I know is if the bike won't go over 4000 - 5000 rpm. There may be others, but someone else will let us know.

[SteveD]

The symptom I've experienced is a bike that runs well, say up to 140kph, but then doesn't go any further. Giving it more throttle there, say at 5Krpm, gives nothing.

Backing off a tad, and all feels fine.

[Jean]

It seems they degrade, not justto the point of having tears or holes. My R100s was just sluggish when I needed to accelerate quickly to pass. When I discovered this, they were at least 15 years old.
One had a real tear, maybe 4-5mm, the other was just limp compared to a new one. I replaced them both.
It made a huge difference in throttle response.
I replaced them again after 10 years. (in 2005 or 6) Once again, the difference in how the old ones FELT compared to new ones was noticable.
And Steve, I noticed the difference BEFORE 140Kph, it happened when I rolled-on from around 90-95kph, (just around 4K rpm) on the first change-out. DANGEROUS, to say the least.

[anyway, before I hit on changing the diaphragms, I got the cleanest carbs you ever saw!!]

[ME 109]

I think the symptoms match the size of the hole/tear.
Big hole/tear will cause a breakdown on the affected cylinder as soon as the throttle is rolled on at any rpm.
A small hole/tear will cause a breakdown on the cylinder to a lesser degree.

Patching a diaphragm with bicycle tube rubber and glue will give a temporary fix.
Many auto parts store will carry a suitable diaphragm that is listed for a land rover or range rover?? I think they fit a stromberg? carby.

[SteveD]

The Stromberg CD150 diaphragm fits a 32mm Bing, and a CD175 fits a 40mm Bing.

ME109 said...

Patching a diaphragm with bicycle tube rubber and glue will give a temporary fix.

I hear a condom will also do that as a temporary measure. The black ribbed ones work better if you turn them inside out!

airheads.org

The whole REASON for finding and using Stromberg diaphragms is that on certain R bikes (the R80/7 is one), the BMW dealer will not sell you the diaphragms alone, but will tell you that you have to buy the whole slide assembly with diaphragm attached. This is on carbs where the diaphragm is attached to the slide by a pressed-on nylon ring.

However this ring can be pried off fairly easily with a screwdriver and your fingers. Just be careful not to scratch the slide. The Stromberg diaphragm will then fit on precisely, and the nylon ring can be pressed back into place.

[Chuey]

Cool info so far. I hope Rob doesn't mind my using his name as an excuse to ask a question that came up when I read that he needed a new brain. It could be called attempted humor.

Chuey

[Deleted User 287]

I don't mind, but it will cost you one good bicycle that fits me, delivered to my door.

[Garnet]

Many auto parts store will carry a suitable diaphragm that is listed for a land rover or range rover?? I think they fit a stromberg? carby.

Hard to find these fuel injected daze.

1 1/2" Stombergs from a Spridget = a 32mm Bing

1 3/4" Stombergs from an MGB or 69-70 Volvo = 40mm Bing.

I bought up all the ones I could get 3 years ago for 80 cents each when my supplier discontinued them. Now I have to buy a Stomberg carb kit to get a diaphram, still cheaper than Bing or BMW. For those who say they are inferior, I say "show me the BMW logo". BMW (or Bing) never made carb diaphrams, they allways bought them from someone.

[ME 109]

Years ago my brother holed a diaphragm on his RS on the way to the Ghost Town rally at Silverton (Aus)
It was fortunate actually because all the acquired repair knowledge came in handy the next day, when my RS did the same thing.
Seems an awful waste for a condom tho' Come to think of it, we may have used puncture repair patches.
I asked my wife if it was ok to carry a condom on the bike for diaphragm repairs
She said if I did, I could use it to repair other bodily injuries too.
Not sure what she meant.