"Beefier" Airhead Diaphragm

[snoop]

You can get a "beefier" diaphragm from stromburg carbs as replacement for the bings.
The carbs in question are the CD150 and CD175 for the 32mm and 40mm Bings.
From Moss Motors, the part numbers are 365-320 and 366-040. Tthey are $20.10 each for the CD150 and $3.95 for the CD175.
(thx to Bam Bam)

From the sticky dark secrets thread.


Does anybody have experience with these, I ripped mine trying to get it out and need a replacement. It looks like bmw doesnt sell these seperate anymore.

[Stagehand]

you can get them straight from Bing, no problems.

Why the hell is one 20 bucks and the other one $3?

[TaterHarry]

Order them from Bing if you must. That said I think the dealer still carries a full rebuild kit either with or without the diaphragms, so you might go that route. The "beefier" Stromberg diaphragms are also stiffer, and are not recommended except in an emergency IIRC.

[Stagehand]

just saw eubmw's got whole Bing carb kits for under $30

[Beemerboff]

A little stiffer isnt necessary a bad thing .

One of the true secrets to tuning CV cards is selecting the correct slide spring / needle combo

Bing has a choice of one spring and around two needles, so no problems with selection here , but SU has a choice of eight springs and 600 needles, so you have lots to play with.

A stiffer spring/ diaphram will richen the mixture in transition , so you could probably drop the needle a notch , and get better throttle response and gas mileage at the same time.

[jtwind]

Originally Posted by Stagehand

just saw eubmw's got whole Bing carb kits for under $30

Maybe a heads up here. I had a buddy buy some parts from these guys. Most of what he bought was not Bing or BMW stuff. It was aftermarket crap. He installed pushrod seals from these guys and all 4 split from top to bottom shortly after being torqued up and running. Can't say for sure about all their parts or carb parts, but asking if they are BMW or Bing parts maybe a good idea. Trying to save a few cents for some of this stuff can backfire. Some of the stuff is cheap for reason.

[Stagehand]

excellent point.

well taken. :cool2

[SOLO LOBO]

Originally Posted by jtwind

Maybe a heads up here. I had a buddy buy some parts from these guys. Most of what he bought was not Bing or BMW stuff. It was aftermarket crap. He installed pushrod seals from these guys and all 4 split from top to bottom shortly after being torqued up and running. Can't say for sure about all their parts or carb parts, but asking if they are BMW or Bing parts maybe a good idea. Trying to save a few cents for some of this stuff can backfire. Some of the stuff is cheap for reason.

I ran these carb rebuild kits in my old R100RS, and then in my old R100GS since 05/2006 with no issues and have a set of rebuild kits on the bench from them for my R80G/S... I do keep the diaphrams I pull out as emergency spares on the bike to rescue myself (or any other 32mm bing carb users...)

[soyanarchisto]

I bought carb rebuild supplies from eubmw and had no issues whatsoever. Still going strong.

[bikecat]

Came across this thread as I am starting a carb rebuild.

Any further reviews on the EUBMW rebuild kit? I realised that I bought them about a year back when the bike was still very much work in progress.

Will get the jets etc from Motobins, I reckon. Pound is low now and might as well take advantage of that.

Cheers

[squish]

Originally Posted by Beemerboff

A stiffer spring/ diaphram will richen the mixture in transition , so you could probably drop the needle a notch , and get better throttle response and gas mileage at the same time.

Wait a second, how would this work?
A stiffer spring and or diaphram would be resistant to lift under increased intake vacuum. (When you give a CV carb more "gas" what you really are doing is giving it more air. your opening a butterfly that allows more air into the intake tract which causes the slide and needle to lift.)

If the slide's not lifting, it's not flowing more fuel (since the needle is further into the needle jet effectively blocking more gas from coming up the emulsion tube.

Seems to me what happens is it makes the engine a slight bit more sluggish to respond to intake vacuum. Which in turn makes the rider dial in more throttle for a given increase in engine speed.

[One Less Harley]

I agree w/ squish on this.

and when does running richer mean BETTER mileage??????

[Beemerboff]

Read my post again .

If the butterfly opens faster than the slide there is more air flowing in the same space, faster flow therefore more suction at the needle jet, more fuel sucked up and a richer mixture in transition, where it is needed.

Faster flow is beneficial too - just look at the problems fuel injected bikes have at low flow - they just dont have to flow speed to fuel properly.

At steady speed , no movement of the butterfly, the stiffer spring / diaphram will still hold the slide a little lower, richer, but the difference is not as marked as during transition.
As most carbs run plenty rich at a steady speed they can be leaned off here to benifit, and if this can be done without a detrimential effect during transition then higher mileage is possible.

Fitting a stiffer slide spring and lowering the needle is one way of doing this - there are a choice of 8 springs availible for SU carbs and the selection of the correct one is one of the secrets to tuning a CV carb.

But you wont read about it anywhere but here, I got it verbally from the guy in carb specialists Midel in Sydney when I was working on a good set up for 2" SUs on a Datsun Z, and I have never seen it in print anywhere, including in the books on tuning SU carbs.

But then I have my own views on a lot of things, so ignore them if you wish - I am used to being told I am wrong and I wont mind one bit.

[One Less Harley]

At steady speed , no movement of the butterfly, the stiffer spring / diaphram will still hold the slide a little lower, richer, but the difference is not as marked as during transition.
I'm more than willing to learn...but a lower needle means leaner...doesn't it??? Unless I'm missing something??? Just doesn't seem right, but I'm rather heavy handed on SU's, be that Hitachi's, ZS's or Bings. So, your saying more fuel due to suction even with a lower needle..hum, never thought of it that way, better atomization too

[squish]

Originally Posted by Beemerboff

If the butterfly opens faster than the slide there is more air flowing in the same space, faster flow therefore more suction at the needle jet, more fuel sucked up and a richer mixture in transition, where it is needed.

Faster flow is beneficial too - just look at the problems fuel injected bikes have at low flow - they just dont have to flow speed to fuel properly.

At steady speed , no movement of the butterfly, the stiffer spring / diaphram will still hold the slide a little lower, richer, but the difference is not as marked as during transition.
As most carbs run plenty rich at a steady speed they can be leaned off here to benefit, and if this can be done without a detrimental effect during transition then higher mileage is possible.

*Snip*
But then I have my own views on a lot of things, so ignore them if you wish - I am used to being told I am wrong and I wont mind one bit.

essh...
Ok here's the deal the lower the slide is in the carb the less air and fuel is traveling through the Carb.
Basic quick primer on CV carbs..
The butterfly controls the amount of air that CAN come into the carb.

The slide controls the amount of air and fuel that go into the combustion chamber.

See the needle(also Jet Needle) is connected to and moves in conjunction with the slide.
If that slide doesn't lift there's going to be less fuel, not more.

That is because the needle sits in a device called the emulsion tube. which at the other end sits in the float bowl into the fuel that's there, the tube is capped off by a device that's called the Needle Jet (also called the Main jet or just the "main"). This is the first part of the fuel metering system.
The second part is that needle, it's got a taper on it. and it's controlled by the slide, as the slide moves up. the needle is pulled up. this allows more fuel to flow up the emulsion tube and be "sucked" into the flow of air that is heading into the combustion chamber.
Intake velocity's not going to matter that much when the needle is working like a plug in the emulsion tube.

Originally Posted by chinesescooterreference.com

Second, at least here in the US
Carbs are set very lean at idle and lean in the mid range and almost rich on the top.
Mid throttle settings, that is the slide has just lifted and the fuel is almost all being metered by the jet needle and needle jet.
are most often lean or maybe just a little past lean toward rich.

As for fuel injection bikes.
One of the biggest areas where FI controlled engines work is at slower engine speeds or when an engine is cold,
The can produce the correct amount, and often with better fuel atomization then a carb can.

The biggest drawback to lots of FI systems is how abrupt the fueling is compared to the rather unsophisticated CV carb system is.
Depending on how the FI system is controlled this can lead to surging
Like early BMW oilheads.