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Old 02-22-2012, 06:00 PM   #31
supershaft
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Quote:
Originally Posted by pcarnut View Post
Just getting back into airheads so this is timely. How does one change the needle if so inclined? I had the slide out but couldn't see how to get the needle out to adjust the clip. And where do you get alternate idle jets, dealer didn't stock them so do I have to contact Bing?
No dealership should be selling parts over retail IMO but some do. Max BMW list current retail. I wouldn't think Bob's is but I haven't checked. I do most all my business with my local dealership. SFBMW has a great parts dept. Lots of airhead parts in stock. The parts manager there is the only parts manager I have worked with that actually auto orders. I have known many that claimed they did but . . . . If they sell more than two a quarter or whatever the auto order mandate is, it actually gets auto ordered. You can't ask for anybody to do more than that and stay in business. Any dealership should have parts not in stock in stock in about a week or let you know if it is coming from Germany. That often use to be faster than down the road but not any more.

Look up the PN's yourself. Read them as BMW groups them. Two numbers at a time, then two more, then one, then three and then three again. It works!! They are so much easier to read and hear that way! Doing it by the book, you can rail through dozens of PN's and not get a single one off with a decant parts guy at the other end. Quantity first or last? I find that depends on who is typing them in. I always say the word "quantity" then whatever the number is.
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Old 02-22-2012, 09:32 PM   #32
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My thread's done been hijacked a little so I'ma recast:

Quote:
Originally Posted by helion42 View Post
in this trip I'm planning, I'm going to be going from 5-6k.ft. @ low humidity, and then staying at ~500-700 @ very high humidity for quite a while. I'd figure there would at least be an adjustment with the mix screw?

I've found a Bing chart but it's not very helpful as it's for aircraft. It seems the only source for the manual for bikes is from Bing?
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Old 02-22-2012, 10:42 PM   #33
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Originally Posted by ignatz72 View Post
It will depend on what bike/carbs you have (picts of the parts help!), but if you have Bing CV carbs you should see either a plastic screw or a clip around the needle at the bottom of the inside of the slide. Removal of the clip should be self-evident, but if you have the plastic retainer with a screw head, just use a phillips head screwdriver to unscrew it a bit, in both cases the needle should then be free.

You can get the stock jet for your model from Maxbmw.com or others as mentioned here, but if you want to get crazy with jets, your best bet probably would be to call Bing US. Max carries a few sizes of jets for the few bikes I checked, but may be able to special order others.

You might want to call Bing to get the proper jet for your application, then order that jet elsewhere as Bing can be pricey.
Couldn't see any screw or clip either above or below the slide. Not looking to change them right now, just confirm they hadn't been changed. I'll try going up one size on the pilot first.

Quote:
Originally Posted by supershaft View Post
No dealership should be selling parts over retail IMO but some do. Max BMW list current retail. I wouldn't think Bob's is but I haven't checked. I do most all my business with my local dealership. SFBMW has a great parts dept. Lots of airhead parts in stock. The parts manager there is the only parts manager I have worked with that actually auto orders. I have known many that claimed they did but . . . . If they sell more than two a quarter or whatever the auto order mandate is, it actually gets auto ordered. You can't ask for anybody to do more than that and stay in business. Any dealership should have parts not in stock in stock in about a week or let you know if it is coming from Germany. That often use to be faster than down the road but not any more.

Look up the PN's yourself. Read them as BMW groups them. Two numbers at a time, then two more, then one, then three and then three again. It works!! They are so much easier to read and hear that way! Doing it by the book, you can rail through dozens of PN's and not get a single one off with a decant parts guy at the other end. Quantity first or last? I find that depends on who is typing them in. I always say the word "quantity" then whatever the number is.
Good info, thanks!
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Old 02-23-2012, 10:03 AM   #34
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Quote:
Originally Posted by helion42 View Post
My thread's done been hijacked a little so I'ma recast:
The answer was if only a couple thousand feet then don't worry to much, if you are just passing threw. If staying at a different altitude then you might reconsider, that is dependent on how different it is.

Did your question ever include a specific altitude change you are expecting to make? The CV carbs will make some adjustment for even 5 or 6 thousand feet or more if passing threw again. Expect that these carbs will burn leaner the higher you go so might be a good idea to keep your eyes on the plugs. Ultimately it is plug color that we depend on to tell us how the carbs are doing.

There was one rider reported climbing Pike's Peak with carbs set for 4,000 feet, or something like that. Certainly doable with Bing CV's. But if you were moving to Pike's Peak you might want to rejet.

I think I got that right. Somebody is sure to correct me if not.
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Old 02-23-2012, 10:58 AM   #35
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Engines burn richer with altitude, this is because the air less dense and has less oxygen.

running richer is one reason why an engine will lose power with height, but the real reason is because gas needs oxygen to burn properly and at 15/16k ft you will be running at a power loss of around 40% (i think).

Jet engines can run at higher altitudes as they can suck in vast quantities of air, im not sure what the maximum altitude of any piston engine is But i think about 30-35K ft.

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Old 02-23-2012, 11:09 AM   #36
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To clarify, I am just passing through a high point. The altitudes I'd be spending more than, say, 24 hours at are ~5000ft and seal level (Riding about in Cali for a few weeks). it's adjusting for sea level and the inherent humidity change that I've been asking about.
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Old 02-23-2012, 01:51 PM   #37
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Well I think you'll be OK. Sea level to 5,000 feet should be with in the capabilities of the CV carb. If you have time and want to check, just pull the plugs and see if they have changed color.

Humidity? I remember you asked that. There is not a carb function or adjustment for humidity that I have ever heard of. Is this something you get from Hot Rod magazines? Could be they have a factor for humidity, I don't know, I stopped reading Hot Rod magazines when I was in my 30's I think. There is an old trick of "water injection" that I always wanted to build but never found the proper pieces to make it work. You can spray water in the carbs on a running engine and it is supposed to clean the carbon out or something. So high humidity will maybe make for cleaner running. Some engines do run better in the rain, ever notice that? As a general rule I wouldn't worry about humidity.

I thought the deal was air pressure. The higher altitude has less air pressure, the diaphragm lifts the slide less and therefore the needle rises less. Less needle rise is less gas, equals leaner burning. But I really don't know.
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Old 02-23-2012, 06:19 PM   #38
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Humidity plays into the ideal gas law and the law of partial pressures; Atmospheric gas density changes with altitude and temperature (PV=nRT), but also the %water vapor will change the %O2 (partial pressure). If I were somewhere that was high altitude and high humidity (like parts of PNWest), the O2% would be thinner than similar at low humidity.
However, if I'm at sea level, the added humidity would ..raise the practical altitude by a bit....

lol I think I answered my own question by suddenly remembering my chemistry class.

I've heard of water injection in hardcore turbocharger systems, the mist of water cools the charge and densifies it, making it possible to cram more air in. I don't know shit about what it does on carbureted cars

Quote:
Originally Posted by disston View Post
Well I think you'll be OK. Sea level to 5,000 feet should be with in the capabilities of the CV carb. If you have time and want to check, just pull the plugs and see if they have changed color.

Humidity? I remember you asked that. There is not a carb function or adjustment for humidity that I have ever heard of. Is this something you get from Hot Rod magazines? Could be they have a factor for humidity, I don't know, I stopped reading Hot Rod magazines when I was in my 30's I think. There is an old trick of "water injection" that I always wanted to build but never found the proper pieces to make it work. You can spray water in the carbs on a running engine and it is supposed to clean the carbon out or something. So high humidity will maybe make for cleaner running. Some engines do run better in the rain, ever notice that? As a general rule I wouldn't worry about humidity.

I thought the deal was air pressure. The higher altitude has less air pressure, the diaphragm lifts the slide less and therefore the needle rises less. Less needle rise is less gas, equals leaner burning. But I really don't know.

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Old 02-23-2012, 06:46 PM   #39
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This months, March, Air Mail like all months has Oak's column, Airtech. He has a good article on "Altitude Carb Jetting". Talks mostly about which jets to use, change. I won't attempt to repeat everything and it would not be right to quote it all I think, you do belong to the AirHeads don't you? I will quote one sentence, and hope this is not too much out of context, "The CV carbs are pretty much self adjusting in design for altitude changes."

The articles by Oak in Airmail are often mentioned as the main reason for belonging to ABC.

Charlie
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Old 02-23-2012, 07:44 PM   #40
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I thought we had already answered h42's questions. If it's jetting right for sea level, there is no need to re-jet. No need to re-jet for humidity either. That seems to be the consensus.

Oak is giving the myth more fuel. It is one long tale. Here is another try at myth busting:

CV carbs do not self adjust for altitude. What they do they do at all altitudes. They don't allow the slide to open any more than the engine needs regardless of altitude. The higher the altitude, the less they will allow the slides to open. It is all nothing that can't be done with your wrist and slide carbs if you pay attention to your engines throttle input needs. Why twist the throttle open more when it slows you down versus speeding you up. You have to monitor your slide type throttle input at sea level just the same to a lesser degree. Only CV carbs allow you to get away with wacking the throttle open no matter what the engine needs at sea level or high altitude. The only thing they self adjust for ANY altitude is proper throttle input with the jets it has and that isn't jetting. It's proper throttle input with the jets at hand. CV's don't self adjust. They self restrict throttle input. Nothing a smart wrist can't do.
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Old 02-23-2012, 08:46 PM   #41
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Same thing shaft said in different words:

The general operating principal of a carburetor requires a pressure difference between one side and the other. The vacuum on the engine side of the carb is required to pull fuel through the needle and idle jets as well as create enough turbulence to atomize it. If you rapidly open the throttle on a slide type carb you create a momentary loss of vacuum. At higher revs the engine will just bog momentarily. At lower RPMs it will just die. The intent of a CV carburetor is to eliminate the possibility of this condition by controlling the throttle with vacuum. The slide is not operated directly by the rider, but instead is operated indirectly by vacuum. The rider opens the butterfly thereby allowing engine vacuum to lift the slide. In this manner the slide will never open fast enough to lose vacuum as it requires presence of vacuum to open in the first place

How does altitude affect this? There's less pressure outside the engine and thereby less of a pressure difference between both sides of the carb. This creates a situation where with a slide carb it's much easier to open the throttle too quickly and lose vacuum. Similarly a CV carb will not open the throttle as quickly or as far as it reaches the point where it loses sufficient vacuum to open the slide further. It will not allow full throttle. Some people interpret this loss in power as jetting problems, but in reality it's a loss of vacuum, a loss of the pressure differential that a carburetor needs to operate.
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Old 02-23-2012, 09:20 PM   #42
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same principal was used in SU side draft carbs found first in Britsh sports cars. only oil was used to dampen pistons from raising too fast. rate was controlled by using different weight oils.

in the 1970's stromberg carbs was used in Jaguar, Triumphs, MG, etc. they used similar diaphragms as Bing.

I'm over due on joining the airhead lists
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Old 02-24-2012, 05:59 AM   #43
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Originally Posted by _cy_ View Post
same principal was used in SU side draft carbs found first in Britsh sports cars. only oil was used to dampen pistons from raising too fast. rate was controlled by using different weight oils.

in the 1970's stromberg carbs was used in Jaguar, Triumphs, MG, etc. they used similar diaphragms as Bing.

I'm over due on joining the airhead lists
I think you can join the Airlist still from the ABC page. Here's a link;


http://www.airheads.org/
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Old 02-24-2012, 09:57 AM   #44
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I've joined almost every free forum and club, haven't joined ones like the ABC cos $25 right now is better spent on the bike. I'm on bimmerforums, r3vlimited, E30tech, ( all for the E30), ADV, VBMWMO, and have tried to register for BMW MOA but the account is screwy for some reason.

Sorry if this is a pain in the ass to continue asking.
the current jets in the carbs are stock for what I'm assuming is sea level, or just plain ol' stock with a 135 main jet. the idle jet is like a 45.

Bing emailed me back after I asked this, they say "At 5,000 feet we would use a multiplier of .95 on the main jet. So, if the main jet is a 135 X .95 = 128 Main." and suggested I purchase their jetting chart and manual for adjusting the mixture screw etc. for long-term stays at a certain altitude.
I understand that they adjust themselves essentially, but am just looking to know how to adjust these when needed according to the spark plug reading.

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Old 02-24-2012, 10:31 AM   #45
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Just an .02: I use stock jetting at 6500' for all jets. My air screw is just about stock as well per the Bing manual. IMHO the Bing Manual is worth having.
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