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Old 10-25-2014, 10:57 PM   #1
JstCruzn86 OP
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Early (32/ 3 & 4) Bing Carb Missing Diaphragm Springs

I think I may have found the reason as to why the bike stalls when decelerating, and pulling clutch lever. Upon inspecting the inside of the carbs, there seems to be no diaphragm springs. Or is this normal for the early type carbs?

Main and idle jets are clean. Floaters looks okay. Fuel level looked okay when I pulled the bowls.

One more thing, the "piston" that slides up and down within the carb body, it has a curved cutout on the bottom and two holes on the edge. Where should these holes be facing? There doesn't seem to be any anything that prevents rotation of that piston, unless air flow naturally keeps things aligned?
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Old 10-25-2014, 11:16 PM   #2
disston
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The early CV carbs did not have slide springs. They can be added and help a return to idle when releasing the throttle.

The piston has a direction or orientation to the main carb body. It is determined by the correct placement of the diaphragm. Index tabs in the rubber diaphragm keep the parts in correct alignment.

You have the earliest CV carbs.

Is this bike an R75/5? That is the bike those carbs came on.
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Old 10-26-2014, 01:20 AM   #3
JstCruzn86 OP
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Quote:
Originally Posted by disston View Post
The early CV carbs did not have slide springs. They can be added and help a return to idle when releasing the throttle.

The piston has a direction or orientation to the main carb body. It is determined by the correct placement of the diaphragm. Index tabs in the rubber diaphragm keep the parts in correct alignment.

You have the earliest CV carbs.

Is this bike an R75/5? That is the bike those carbs came on.
Yep, 1970 R75/5. I see the little rubber tabs now in the underside of diaphragms, one-way fit is right.

Dang, if these early carbs shouldn't have springs after all then the gremlin has once again evaded my detection. Do you know what the purpose of the springs in the later models were? I wonder if they could cure off-throttle stalling?

Thanks Disston
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Old 10-26-2014, 04:13 AM   #4
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The big fat springs above the carb slides are not a cure all for anything but they help a return to idle for some. The effect was not too drastic on my /6 but it did help. Others say their carb performance was dramatically improved. Don't expect miracles. Especially since you have the 3 & 4 carbs.

13 11 1 335 324 early spring, thicker

13 11 1 338 134 late spring, thinner

You should try to find the older threads about problems with the 3 & 4 carbs. Do you still have the spring return enrichners? These were a problem and there are other issues I think. I'm sorry I can't help more but I don't have those carbs I only have heard about it.
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Old 10-26-2014, 04:16 AM   #5
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I have played around with those springs on my R90, and found that fitting them was not a good idea, harder starting and poorer gas mileage.

If you do decide to fit them, get everything working properly first.
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Old 10-26-2014, 04:38 AM   #6
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As has been said the locating tabs on the diaphragm determine the orientation of the slide... provided the diaphragm has been correctly fitted. The hole at the bottom of the slide communicates the vacuum signal to the upper side of the diaphragm and it is important for correct operation that the hole faces towards the cylinder head.
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Old 10-26-2014, 05:01 AM   #7
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Fitting springs should improve off closed throttle stalling, but only if everything else is correct. The spring will delay the movement of the piston relative to the butterfly and the intake air velocity will be increased, and it is intake velocity which determines how much fuel is sucked up past the needle. So the spring acts a little like and accelerator pump on a smoothbore. If you have a Haynes look at the settings for the bikes which did not have springs, and those that did, and you will find a few changes, so if you add the springs it might be as well to consider changing the needles and jets to suit. But a try with the early springs and the needle moved a notch wont harm anything. Last time I bought them the later springs were stiffer than the early ones, but I have fine tuned my bikes with SU springs - they have a choice of over a dozen so you can get it just right, if that is your preference. FWIW none of the previous posters understands the basic functioning of a CV Carb, so their postings are largely irrelevant, and they should really try and understand the principle behind these things before they spout off.
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Old 10-26-2014, 05:47 AM   #8
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Quote:
Originally Posted by Beemerboff View Post
FWIW none of the previous posters understands the basic functioning of a CV Carb, so their postings are largely irrelevant, and they should really try and understand the principle behind these things before they spout off.
If that includes me would you care to explain why every Bing CV slide has the diaphragm vacuum hole towards the cylinder head/throttle valve side of the carb. The OP did ask about slide orientation.
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Old 10-26-2014, 06:22 AM   #9
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The flat top Bing carburetors on my 1978 do not have a piston spring. Gravity moves the piston. If the carburetors are designed without a spring, it is unlikely adding one will help. But, if your hobby is redesigning carburetors - then go for it! Good luck!


Edit: re-reading the last two questions: the holes in the bottom of the piston should face the intake valve (or throttle butterfly valve). The diaphragm should have a notch that fits in the carburetor body to keep the piston aligned.

Stan_R80/7 screwed with this post 10-26-2014 at 06:38 AM Reason: added comment
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Old 10-26-2014, 10:10 AM   #10
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When you guys say early 32, what years are you talking about? My 1975 R90 doesn't have the springs and yeah, sometimes it seems to be off in lah-lah land about having the idle speed fall to where it should be.

I use the engine to bring idle down sometimes (if you pull in the clutch, no throttle it'll sometimes idle at 2000+ RPM) where I bring the RPMs down while engaged in gear.

But do the springs screw up 'take off' (or help it) if you install them where they weren't designed to go?
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Old 10-26-2014, 10:38 AM   #11
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I think that the springs were fitted to the bikes that came out shortly after yours, I don't think that the carbs themselves were that different, but as me beemergrumpy has pointed out the jetting and possibly the slide shape need changing if you are going to be successful.

IMHO just fitting the springs to the earlier carbs is unlikely to help. Sticking idle is often due to either adjusting idle mixture on a bike that is not fully warmed up, or due to the AR unit on the points sticking.
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Old 10-26-2014, 10:56 AM   #12
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I think (but am not certain), that the older model carburetors were intended for slower idle speeds. I have noticed that if I raise the idle speed too much (> 1200 rpm) there is more of a tendency for a high 'sticking' idle. I replaced the points with a Boyer ignition, so ignition advance sticking is eliminated. My interpretation of this is that the idle circuit becomes less in control of the idle at higher idle speed because the butterfly is opened too much. The Bing carburetors seem really simple, but that is only because much thought was put into their design.

The addition of springs (I think) will allow a higher idle without the 'sticking' effect seen with the older model carburetors. But, as others have pointed out, adding a spring changes the carburetor. If someone were determined and methodical, I expect they could sort out the issues from adding a spring to the earlier models.
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Old 10-26-2014, 12:08 PM   #13
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Originally Posted by Stan_R80/7 View Post
My interpretation of this is that the idle circuit becomes less in control of the idle at higher idle speed because the butterfly is opened too much.
The danger of having the butterfly open too much is that it may start to bring the by pass or transition ports into play which could lose control of the idle speed as they are not restricted by the mixture screw. I believe this can be the cause of an idle that hangs up and it may happen if an attempt has been made to reduce the idle speed by adjusting the mixture screw and then the butterfly has been opened up to compensate.
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Old 10-26-2014, 12:32 PM   #14
Bill Harris
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The reason for the springs in later CV carbs was to ensure positive and consistent return of the needle-slide. Earlier carbs relied on gravity and the weight of the slide and the decrease in vacuum across the venturi to close-- return the slide. This caused mixture problems if the slide/jet-needle were still in a elevated position when the airflow requirement (ie, the butterfly valve) went to a low setting.

I don't know if slide springs can be retrofitted.

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Old 10-26-2014, 12:53 PM   #15
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Quote:
Originally Posted by Beemerboff View Post
Fitting springs should improve off closed throttle stalling, but only if everything else is correct. The spring will delay the movement of the piston relative to the butterfly and the intake air velocity will be increased, and it is intake velocity which determines how much fuel is sucked up past the needle. So the spring acts a little like and accelerator pump on a smoothbore. If you have a Haynes look at the settings for the bikes which did not have springs, and those that did, and you will find a few changes, so if you add the springs it might be as well to consider changing the needles and jets to suit. But a try with the early springs and the needle moved a notch wont harm anything. Last time I bought them the later springs were stiffer than the early ones, but I have fine tuned my bikes with SU springs - they have a choice of over a dozen so you can get it just right, if that is your preference. FWIW none of the previous posters understands the basic functioning of a CV Carb, so their postings are largely irrelevant, and they should really try and understand the principle behind these things before they spout off.
Needles and jets? What needles?

In general? I don't have any experience experimenting with springs. I do have a lot experience in figuring out that carbs in general have to be adjusted just so so in order to work right. Our Bings are no exception. 1200rpm idle is borderline too high for any carb early or late if you don't want it to fast idle when good and hot. Sticking advance units? It happens but it's most often carb settings.

Advance unit's? Their issues are often not about sticking but rather about not being set up right. A lot of ignitions are set at max advance. That very often leaves the ignition advanced at idle until the advance is adjusted to work properly. Setting them at max advance is better than setting them at idle? Maybe. Having your advance until setup to do both at the same time is what they are designed to do and what they should do and what is best. The advance units often need tuning but the topic hasn't got rolling on the idiotnet yet. Maybe this will help?
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